Why would you need a trisynch for Mame? makes no sense to me at all. I used a 27in Monivision VGA for Mame. 
Off the top of my head:
Mid-res games (Super Sprint, Paperboy, 720, Bonanza Bros, Virtua Racing, etc)
Vertical games of 288 lines or more (ie without monitor rotation)
VGA/games run at 480 lines (Spy Hunter, Tron, Tapper, Rampage, etc)
You can also run interlaced 1024x768 with a trisync for PC games.