This depends. If you are tracking with 'phones, this can be OK to listen for artifacts (hums, buzzes, ticks, etc.) that you don't want to have ending up on the track. But for mixing? NO. Headphones don't work well for that , they exaggerate your stereo field, as well as hype various frequency bands, and this will cause you to make wrong decisions in the mixing process. You really need to treat your listening space and use decent, playback speakers to mix.