If the soft contacts are not designed for day and night use, your eyes will end up being very dry and lack of oxygen. You may have swollen eyes in the morning. If you don't want to take the trouble of taking them off before sleeping, you can choose the RGP contacts which have a better oxygen permeability.
If you sleep with soft contacts, they will dry your eyes out and make them irritable when you wake up in the morning. You may get eye infection because the contacts in your eyes will get dry and dirty. And you may feel pain to take them out.