Generally I dont pre-wash, certainly not with 2 bath developers or extremely dilute developers (Rodinal 1:100/1:200) and in most cases it does not make a difference.
With certain developers it does make a difference, PMK and Pyrocat HD are two. I tested the Pyrocat HD with and without prewash (5 min cont. agitation) and the density change was significant.
Most modern films, as stated, probably does not need it with stock developers (D76 etc), but when you get into the extreme dilutions you need to compensate for the additional water from the pre-washed film (anything from 4-6 ml/roll). The anti-halation layer should not affect the developing process (it is on the "back" of the film) and with stand and semi-stand developing you leave the film in it long enough anyway.
It is a way of getting rid of some dust though - cameras tend to accumulate it and it then, of course, it migrates to the film (and with unswerving accuracy ends of in the areas that are difficult to spot!).
The trick is to be consistent, either do it all the time or not at all. At least then you have removed one variable in the process.