Experimentation will always have a purpose, whether that's to further a craft, myself, my crew, my equipment etc.
There are two types of "Experimentation". The first being the primary outings of the film-maker, the first few times when he/she ventures into their field, tests their boundaries and discovers if their chosen profession or hobby is indeed for them. I would call this purely a practise in practise, rather than a form of experimentation, albeit very, very similar.
Secondly, "Experimentation" in the sense of an experienced film-maker. To experiment beyond their genre, style, and like i said above, beyond their boundaries for multiple reasons.