Overheads are used to capture the room/space & the overall blend of the instruments in their range. A completely close-miked drum set can sound a bit artificial if you only use those close-miked sounds; mixing in a bit of the overhead sound sort of glues the whole thing together. Also a lot of the time people don't put mics on everything, so you might just have one on the kick, one on the snare and the overheads for the rest. Orchestral recordings are often done with overheads as well.