In this league, there aren't a lot of good free agents and when guys come out of nowhere they are usually picked up quick.
If people are adding and dropping all the time, they are likely to lose a decent player.
Also, anyone picked up automatically counts as a year towards the 40 salary cap. If you pick that player up with 40 or under years, you can keep them as free agent if you want (it is how I got Sanders) but if you pick them up after 40 they go to free agency (it is how I lost Harris/Butler and had to bid $74 for Henson).
I think this rule should stay as is. IN the NBA there is no minimum/maximum adding/dropping players and once above salary cap they can only be signed for minimum (forgetting about exceptions).