Taking articulation to mean the ability to say clearly whatever one wishes to say, its importance is obvious. The desired effect itself, of course, may or may not involve actual precision or clarity. Sometimes an imprecise or vague effect may be the intention. Assuming you mean the word in the first and strictly correct sense, then yes, it is very important to me because I don't want to attempt to say one thing at the piano and accidentally say another.
Mind you, lack of correlation between conscious intention and effect isn't necessarily a bad thing in improvisation. This is because improvisation depends heavily on the unconscious and on constantly surprising oneself. So my answer has to be qualified in this latter regard.