Do androids dream of electric sheep...

In the original probably even Call sleeped, and it would make sense to reduce wear/regenerate, save energy, etc. Computers had for decades sleep modes where only memories are powered to not lose data. The ships were automated enough to work on their own.

In the new ones, David had a mission to learn the ancient languages to be able to communicate and to be able to provide us background about Shaw, so him being awake for 2 (?) years might be justified. I can not find however no justification for Walter being away for more then 7 years other that to imply that he is a slave and has to toil arbitrarily. Further more, if David went insane with maintance for ten years, what says a 7 year trip like that would not give the situation. 

someone had to be awake to tend to the plant life on board the covenant plus the value of the embryos may have dictated someone be awake incase something went wrong that muther couldn't deal with. as we see in AC, Walter removes what I assume are a couple of dead embryos which is something muther couldn't have done.

You both raise very Solid Points.

ASH was on a Secret Mission and had to keep his True identity as a Synthetic Secret.

David and Walter would have had Tasks to do during the Journey.

Bishop is the Interesting One and while he can Enter Some kind of Sleep Mode, would he need to be in Cryo-Sleep to do so?

We cant rule out Bishop would have awoken between to attend to duties but we can SAFELY assume the Ship is so Advanced and Automated that this is not required and the Journey was Short.

So Bishop in Cryo-Sleep was just a Plot Convenience to have it that Ripley would not be AWARE he was a Synthetic until he CUT himself with the Knife.

It seems Call was always on in AR. Her true identity was unknown to the crew at first as well- sort of like Ash.