Why stickers instead of printed decoration and vice versa?
I think it depends on series, if set is licensed as well as targeting audience. Sometime printed parts are used in a place where sticker would be hard to apply.

Architecture series, is a good example where stickers are not used since series are advertised as premium product. Duplo and Juniors use printed parts too as these are targeted for young kids.

Licensed sets usually have stickers though. This may be related to the fact that LEGO treats licensed set a little different, where you cannot buy extra item in B'n'P or get a replacement of specific license related item. So it is better having it unprinted and have an option to replace/acquire a part.

Printed elements also limit their practical use (re-use). Stickers give you choice of applying them or not, while printed parts are there forever1. Good example is 42096 Porsche 911 RSR. It has white wheel arches/fenders with unique print for each of 4 included pieces. Non-printed counter part doesn't exist in this color yet, so these may not fit your MOC. The rest of the Technic Panels have stickers. This leaves a lot of room for using them in other creations (if sticker are not applied). Otherwise panels would be rendered useless if all of them would be printed.






Not really