The hint is in the name. The vast majority of deep sky images are exactly that, pretty pictures. Theres no scientific rationale for taking them and no need for the person doing so to worry about gamma stretching or sharpening – its about showing the structures and elegance in an object in a tasteful and appealing way. Look at how many people return to an object (such as M42 or M16) every few years because improved skills, location or instrument mean they will be able to pick out more detail or create an image more eye catching. The target itself has not changed. It is a quest to get the maximum performance from the kit you can afford: we all know that if we had a PlaneWave 24″ in Chile, an Andor camera and unlimited time on it we could take better pictures, but most of us cannot afford one, so we strive to do the best we can.
With planets its also about detecting features (dust storm, cloud feature, polar cap) but, they change which makes life much more interesting.
Its the change aspect that makes variable stars, the Sun, aurora, meteors and comets interesting too. Its why I spend most my nights chasing variable nebulae.
I have seen people post pics in the BAA Gallery that were clearly composites and they have not mentioned it. That I must admit to disliking.