On my hardware, it's probably not profitable. I have a bunch of old/low-end systems, but I mine just to play with the technology and think of it as buying non-expiring lottery tickets. My highest scoring system is a 3.2 Ghz 4 core i5-4570 that's been getting $.10 to $.25 per day mining cryptonight (whatever that is) for the last few days.

At the moment, it's getting $0.18 per day.

As I noted in my response to @alexgr, nicehash does have settings available so that you can mine only when it would be profitable. I haven't actually made use of that capability, though.