The movement to incorporate commas into tp proceeds apace. For the most part, their use is still optional, but it is often appreciated as removing some ambiguity or, at least, adding a certain visual clarity.
Of this latter sort is the spontaneous use of commas with 'la'. While there may be some ambiguities with repeated 'la's, this usage occurs with the more common single 'la', whch do not present any possible ambiguity. The practice of a comma with 'la' arose before anyone actually recommended it or any authority modeled. So, it appears to be either a transfer from English (etc.) practice or a spontaneous aesthetic choice. The only strange thing about this (aside from its unneededness) is the frequent use of the comma before 'la', rather than after, where the grammar and speech patterns put it. Unfortunately, Sonja models this misplaced punctuation, so it has become common. It does, however, destroy the aesthetic virtue of the usage, since it make a premature break in the flow of the sentence.
The more useful use of commas with 'la' has not been widely discussed. This occurs with repeated 'la' phrases and the question of how they are to be grouped. For a variety of logical and practical reasons, the simplest solution seems to be to have each 'la' phrase condition all of the following sentence (develop from the leftmost S in 'S la S'). This is the reverse of the left grouping of modifiers to a head, but the two cases seem different enough to allow for different treatment. Still, there are cases where a left grouping component is appropriate and, in that case, the aberrant cluster could (should) be set off with some mark, and commas seem the natural available choice. The details of all this needs a good deal more research, however.
Another place where commas have been suggested frequently is before the PPs at the end of a sentence, especially when a DO is present. Numerous variants on "ona li pana e sitelen tawa mi' have been cited as justification. The case here is so strong that usually hyperconservative Lope has incorporated a comma here into his latest lesson revision. Thus, "He showed my movie" (as above) is clearly distinguished from "He gave me a picture" ('ona li pana e sitelen, tawa mi'). While usually optional (I am not sure about Lope's rules), this is too useful not to be encourage when there is the least possibility of confusion.
A final place where commas would often help is in modifier strings. So long as these are simple word after word strings, no questions can arise; each word modifies all that goes before it. But the occurrence of a 'pi' phrase means the succeeding more than one word functions as a unit -- but there is not indication how many more than one word is involved. Of course, if there are only two words after the 'pi', the answer is given. But if there are three or more it is usually possible to find a variety of interpretations. In even a simple case like 'soweli pi linja uta tu', it could mean either a beast with two whiskers (unflagged) or two beasts with whiskers (cats)(soweli pi linja uta, tu). Here, the comma serves as the missing right-hand-end mark (RHE) of 'pi' (generally not in writing in languages, though some, at least, are spoken in juncture and other prosodic features). In this case, and, indeed, generally, one solution -- if you have time to revise -- is to move single modifiers -- especially the terminal number, possession and 'ni' -- up to the head: 'soweli tu pi linja uta'. This occasionally does violence to the usual order of types of modifiers (not very firmly established, after all) but makes up for that in clarity. Sometimes, of course, some extensions are not problematic: j'an utala pi ma tomo Atena' clearly includes 'Atena' in the 'pi' phrases, since "it doesn't make any sense" otherwise (a city warrior named Atena is just not in our experience while a city so names is). Sometimes the extension is forced grammatically: 'jan pi lawa pi jan utala' includes 'pi jan utala' in the first 'pi' since otherwise there would not be two words after it and the whole second 'pi' has to go in for that 'pi' to be proper.
Constructively speaking, the key difference is whether the final piece is added to a string which already ends in a 'pi' or not. If it is, it deserves a comma; otherwise, not. So, if we move from 'jan utala pi ma tomo Atena li wawa' to ' jan utala pi ma tomo Atena wawa' we want a comma before 'wawa'. On the other hand, if we started from 'jan utala li tan ma tomo Atena wawa' to get to 'jan utala pi ma tomo Atena wawa', no omma would apply. (The core of this latter comes, of course, from 'ma tomo Atena li wawa'.) Again, the first case might be better put as 'jan utala wawa pi ma tomo Atena', though there are arguments that this says something slightly different, as it surely does in some cases.
Unfortunately, a comma cannot resolve all the issues in modifier strings, since each added 'pi' phrase introduces the possibility of new ambiguities and a plethora of commas may only confuse matter more, without solving all (or even any) problems. Consider 'tomo pi soweli tomo pi jan lona mi'. Uncommaed it says "the house of my friend's dog", But, with a comma before 'mi' it becomes either (and here the complexities really begin) "my house for a friend's dog" or "a house for mine among a friend's dogs" a friend has several dogs, one of them is mine, in some sense -- say that I will get it when it is weaned -- and this is the house for it". A comma after 'soweli tomo' means that it is my friend's dog house (whether or not he has a dog). And, adding a comma before 'mi' to that, makes it mine among the friends doghouses. Of course, context -- even general plausibility -- will often weed out many of these possibilities. But sometimes we want the more remote case and it is nice to be able to force it, although usually moving modifiers around works better: 'tomo mi pi soweli tomo pi jan pona', 'tomo pi soweli tomo mi pi jan pona' 'tomo pi jan pona mi pi soweli tomo' 'tomo mi pi jan pona pi soweli tomo' . Keeping the left grouping as much as possible is an advantage.
None of this is official or even much discussed in the last case. But this is an opportunity to fix up a reasonable set of guidelines.