Unlike a table saw, the band saw blade is thin and will drift. For reasons I don't understand, the blade drifts in, towards the back of the saw. The longer the space between the two sets of rollers, the more drift you can have. For pretty obvious reasons, this isn't an issue until you begin re-sawing lumber. You want a fence that will allow the wood to feed at an angle, following the drift.
FWIW: The best way I've found to help counteract this so far is 1) use a new blade if you're going to do some tall re-sawing or on dense woods, 2) lube up the blade liberally before each cut, and 3) feed it in as slow as you possibly can. Doing this, I managed to re-saw 4" bloodwood on a low-powered Ryobi band saw with almost no drift.
More importantly, take the time to setup the saw. then drift is almost negligible. also buy a good blade. I get 1/32" resaws in 10" resaws on mine without drift. Again I cannot tell you the importance of setup. whether it's your bandsaw, tablesaw, or router table and the miter slots and fence systems in relation to the cutting surfaces.
Intonation makes for better music. It applies at the tool as well, Guitar or saw.
mk