Huge benefit I'd say is the simplicity with your drive train (IE- one fixed cog/one free wheel in the rear and a singular sprocket up front with the cranks).

There are times when switching gears seems beneficial but a SS/FG will be just fine and you will learn to adjust your pedaling and achieve a good cadence.

I've been on this forum shortly but if you're Trek in consideration is around $400ish and you're thinking of getting into a SS/FG then a Mercier Kilo TT from BikesDirect.com will be advised to you.

Good luck, search before you ask but there are tons of good people on here that are pretty knowledgeable and helpful!