As has been mentioned full disk encryption loses a lot of its efficacy if you just put your laptop in standby all the time. I'd add that as long as a faster boot doesn't compromise your system in other ways, why wouldn't you want it?
When hibernating my laptop it writes the memory contents into swap - which is also encrypted. Yes, de-hibernating is slower if contents need to be read from disk. OTOH it's still faster than booting from disk.