Up to a point. You're going to want to get it off the trub (yeast and crud) at some point, as the yeast will go into autolysis after a while, i.e they die off and start eating each other which will produce some pretty horrible flavours (think cooked meat!). About a week is probably ideal, but you can leave beer in the FV for probably 4 or so weeks without any real bad stuff happening (say if you went on holiday or something)
The common term for this is "diacetyl rest", because the yeast assimilate diacetyl that they produce at the start of the ferment. diacetyl is said to impart a "butterscotch" taste.