The other thing I would be careful about letting your little one sleep in the swing is that they may end up with a flat head. I had a friend who let their little boy sleep in his car seat too much and he ended up needing a special helmet to help fix his flattened head. Just a thought
As long as the seat reclines so babies head isn't on their chest it's not usually a problem. What you might run into though, is baby gets dependent on the swinging motion to help them get to sleep and that might cause issues further down the road.
Wow I just came on here to ask about the same thing. My 7wk old daughter just loves her swing too. She will sleep the entire night in her swing! The last two nights she slept a full 7hrs in it...which is great for me but I wonder if I should be allowing it or not. Last week, she was asleep in her swing and I had been expecting her to wake for a feeding soon so I laid on the couch to wait for her to start stirring and I fell asleep, when I woke I realized 5hrs had passed..she slept for 6 hrs. She will sleep in her crib but only for 3hrs at a time. I feel guilty/selfish for letting her sleep in her swing for so long rather than her crib. My mom figures its fine aslong as her head isn't all scrunched up, which it isnt, but I don't know. Anyone else have an opinion on this. I kind of thought maybe just maybe this will help get her into a routine now that she is more wakeful during the day, she may sleep through the night her crib OR it could just make her not want to sleep anywhere but the crib. I don't know, but I sure am enjoying the sleep too.