That 's clear , the difference is not very noticeable.
On older version of mame (0.7x) when i 've tested fes time ago the difference was few hundreds of Kb .
That is not a big problem for most of time. But if you running on very low power PC. (lot of my user recycle their very old PC , to run old classic like donkey kong , pacman.. etc).. when you have only 32 mega of ram. These few Kb can make a difference. At few Kb you can pass the limit where Windows 98 is beginning to swap memory to HD and slow down dractiscally your performance...
But that sure, you're totally right , in most of the case it doesn't make difference.