Editing recordings of improvised music is a very common practice, but one that is not usually pointed out. Maybe I point it out precisely because I like the concept of having unedited improvisations on record. But life is not perfect, and very often performances have both good bits and bad bits. (This is not the place to define good and bad, which are probably somewhat subjective categories anyway.)
Editing is nearly always done in conjunction with at least one of the musicians involved. More often that not, the suggestion comes from them, and I do the actual edit under their supervision. There are circumstances where I edit without consultation, but then I usually submit the end result to the participants for their approval.
Very often, such edits take the form of starting the piece after the start and/or ending it before the end. Since I dislike fades (except very short ones) I look for gaps in the music which can be made to sound like beginnings or ends. Sometimes, there is a weak section in the middle of a piece. The normal technique here is to find a suitable end and start, and end up with two shorter pieces.
It is common to want to take out a very short section. This may be due to a technical fault in the recording, or due to a musicians tuning up mid-performance, etc. In this sort of instance, I try to edit out the offending moment and join the rest together as best as possible, so that it sounds as if nothing has been removed. (This technique is more difficult with rhythmic pre-structured music since one has to try and maintain the beat and structure - with much free music it is unnoticeable.)
In the LP era, one did sometime have to edit things just because they would not fit onto an LP side. With CDs, this reasoning becomes rarer. If a session is too long for a CD and too short for two CDs say, then I would rather try to find some related music to fill out the CDs, rather than truncate some perfectly good stuff.