Should be fine as long as air flow is not blocked. Some towers have vents on the sides. Use your good judgment here.
I have a Packard Bell tower PC - which works fine. It is equipped with useful card reading slors, and front facing USB ports, but there are never enough, and they are not wonderfully conveniently positioned, so I have a clever plan so I can see the sockets more easily.
Can anyone forsee any snags with laying this case on its side, rather than on its base? There are no vents in the sides, but I'm wondering if processor or power supply fans would be affected, or anything else?