The first couple of flights we took we didn't have a bassinet and it was hard. It's hard enough sitting still yourself for hours on end, let alone trying to contain a wriggler!
So for our first 8 hour flight we booked one and wow!!
Pros: Bubs not only has a special place to sleep/ play/ eat in the bassinet, but with all that added leg room mum and dad will be thrilled and you have space to let them crawl around!
Even though gypsy is getting too long for the actual bassinet now, we plan to continue to book it so she has space to play on the ground.
Cons: cost and availability.. They are expensive to reserve and there are usually only 2 or 3 available per flight.