I play a carved bass with orchestral strings, which has lots of sustain. When playing in bluegrass settings, I control note length by left hand muting - either explicitly stopping the note for open strings, or lifting up for fingered notes. Some songs it sounds better to play long notes and let them ring - for example, medium speed tunes in 3 - where I will just be playing on "one" each bar. Other songs really like short notes - for example an uptempo song in 4, I will often play the bass pattern as a series of quarter notes with quarter rests in between; especially if the group I'm playing with seems somewhat rhythmically uncertain, specifying the end of each note as well as the beginning can help to keep it all together.
At this point in my development, I think I would rather have the option of controlling the long sustain than have the sound all damped down and not have the option of playing long notes.
I never have anyone say anything negative about the sustain of long notes when I play long notes.
One last point, though: the sessions where I play a lot of different stuff, lots of quarter note walkup/walkdown patterns, playing on every beat of the waltz, etc., no one says jack to me as we are packing up. The sessions where I play two notes per bar in 4 and one note per bar in 3 and just shut the heck up the rest of the time, everyone comes by and says "man that sounded great, love to hear some good bass playing". Seems like even if you can only play a little bit, you should play less than you know, for best results.