disposables aren't necessary for night time or for going out. i always used cloth at those times. we did, however, use disposables when traveling, mostly because we just didn't know where to store them (and i always felt bad having soiled diapers laying around someone else's house.
My DD got rash easily, that's why I had to use sposies while out--if I couldn't change her soon enough she would get a major rash. She was a frequent pooper and pooping into a wet diaper then not changing quickly enough would do it every time.
I also switched to sposies at night at 6 months because she would scream her head off if I tried to change her at night and I don't think the neighbours (or DH) appreciated that! A sposie would last all night. My daytime system couldn't be boosted enough to last thru the night and I didn't want to pay for a separate night time system.
I think it makes sense not to invest a lot in a CD system till you give it a try and know that you like it and it's working for you. All kids are different (in terms of what will give them rash, how a certain diaper or cover fits them, and how much they pee)