I will have to be in the minority here
. Used safely on a healthy dog, sedatives can make a world of difference on the amount of stress placed upon your pet. If your pet is used to a crate and/or loves its crate - a sedative probably isn't necessary and he'll probably do fine.
However, if you have a dog who hates the crate: stuffing him into a tiny, claustrophobic space with changing air pressures and odd sounds for 4-6 hours, without any release is placing your pet under a lot of unnecessary stress.
I've flown a lot w/ my dogs (neither of them see their crate as "hang out" places). Wylie (7.5 lbs) does really pretty well and stays pretty calm, although he may try to paw against his bag.
Marcel (3.4 lbs, and normally the relaxed one) went BONKERS the first time he flew and I thought I was going to lose my mind. He finally calmed down an hour into the flight - but I could not move a muscle or it would start back up again. The way home, I tried Benadryl (childrens) - which helps a little, but not really enough for him. This summer, we again flew home - Benadryl on the way out and Marcel still was bothered and made noise. So, on the way home - we gave Acepromazine - and it made a TOTAL difference. He could relax, be comfortable, be sleepy - stress free for him and us.
I really didn't want to have to use Ace. - but now realize that it can be used safely. If you go that route, it's probably a good idea to try a dose at home first to make sure your dog reacts safely. [It is never supposed to be used for cargo, btw]
Another thing - both our dogs get reallly hot under those seats - so we brought along those "gel packs" that you freeze and put them in their bags to keep them cool. Security didn't say a thing about, which was great.