Yes? Maybe?
It depends! If you are just talking about typical homework problems, then unless the instructions say otherwise, it's generally assumed that yes, you should reduce your factions to lowest terms.
In the "real world" though, there are probably lots of times when you don't necessarily want to do that. Lets say you are measuring things that are normally divided into 4 parts , i.e., fourths. You might have values like 1/4, 2/4, 3/4, and 4/4, and it might make perfect sense to leave them like that and not reduce them to 1/4, 1/2, 3/4, 1.