I have never used a capsule, my reversible is currently getting it's third use!

The only benefit I can see is that if bubs is sleeping, you can move the whole capsule instead of a transfer. However, this has never worried me and babies usually go back to sleep anyway if they wake. Also just like a car seat, babies shouldn't be in a capsule for any longer than 3.5 hours (ish) without a stretch for their backs etc.