A good speaker question

Over the years ive had speakers come and go in my system and noticed that many times the screws that mount the drivers into the cabinent arent tightly mounted. Ive always bought used and wonder if that was the intent of the speaker maker or is this a case of the screws coming loose over time. Has anyone done any research on sonic differences with a tightly mounted speaker? I would assume that the tighter the mount, the better the sound, but in the last 2 pairs of speakers that I have checked on, they were not tightly clamped.