RAM wise it sure does.
It used gigabytes of RAM, which is unacceptable on many systems.
Firefox is bad enough as it is on RAM usage.
But, yes, you can save a bit on bandwidth and CPU cycles using AdBlock.
I also had some odd things going on that used massed of CPU which I tracked to AdBlock, but that was likely a bug that has since been fixed...
I much, much prefer NoScript, which REALLY removes all crap.
It's more maintenance as I have to grant things to run, but results in really stripped down and quiet pages. I usually get through complicated internet baking sites etc with NoScript, by granting access to the obvious bank-URLs, but nothing else, like Google Analytics etc al.