in a sense no there is no advantage. It's the same (but the same goes with official mame too)..if all the games you run work fine then you can leave it...
in the other sense there may be a big difference. Some games may now working (ex street fighter 3 is now playable from advmame 1.5 on..or a game may be fixed..ex..toaplan games are now working and need samples..but they work closer to the way they are suppose to now. Again if you care about the games running correctly..or running at all. then it is worth it.
The other side of this 3 sided coin is that advmame 3.0..and now 3.1 is truly compatible for the raspberry pi..(it has official support from the developer) and the code is tweaked to be more efficient on the pi now..as .094 and 1.4 were..but you were "on your own." These tweaks may actually give performance boosts and be worth the upgrade. Only you can judge that though.
It is usable in the retropie image..but it has to be done "manually". I did it and it works just fine.
The main difference between mame and advance mame is the video output and display settings. Advmame is designed around getting the "correct" display so that the games look right no matter what monitor, TV, or display you have. Samurai Spirits on a LCD screen looks like crap but advance mame can fix it easily and make it look better (read worse) like it's supposed to look like. Mame itself can do that...but with major tweaking.
More code to load means needing more RAM and CPU. Advmame is based on "old code". Thus less CPU and RAM are needed...great for the pi! However it being "old" you need an old romset..which can be difficult to find and maintain. About the only reason I don't use it %100 even on my PC is because it won't run KI or KI2..something to do with the linux code (thus the pi..however the pi is underpowered for those games)..those games work fine in Windows. And Advmame can be used from the linux frame buffer..thus not needing X (read gui or windows desktop) so it doesn't have the overhead of the desktop chewing up resources that you could be using and getting better performance..again great for the pi. (and yes advmame will run on pure DOS 6.2...The frontend for advmame will run in pure dos mode as well..so yes you can grab that computer from 20 years ago and make an arcade cab out it..don't expect it to run everything of course!..find that in a modern mame! lol)
Basically what i am saying is that whatever emulator you chose to use is not "right or wrong" or "better or worse" just what works for you. Although I have to admit I wish they would make emulators like fastmame again I can run KI and MK full speed on an 20 year old computer the official mame couldn't even do that at the time..again great for the pi)..but I believe on making the most out of what I have..not just upgrading every time I can. With the pi well you have to do that...
(Note I'm sure I am wrong about some things coming from a technical standpoint. This is not written to be accurate..just to be simple and understandable to the people that are not technical

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