I bought some used front rotors and I was about to put them on when I noticed that it was loose,  where the rings that connect the outside of the rotor to the inside,  and I am pretty sure I dont want to but riding around with wiggly rotors.  My old rotor isnt like this it doesnt have any play at all.  So, I was wondering can these rings that hold the rotors together be tightened or are these rotors garbage?

Thanks.

How much play do they have?
Is it side to side or front to back (as seen on edge, as if the rotor were mounted on the wheel)?

Some movement is ok, that is the point of "floating" rotors.

if you got them from Srinath....they were mine....they are fine, i love floating rotors!!!!!

What exactly are the benefits of floating rotors? 

I realize they allow for some play in the inner part of the rotor, but is that the only advantage?

They are fixed only in the direction that they have to: against brake torque. If you imagine a rigid rotor whith only minimal sideways inacuracy you can imagine what kind of vibration it would induce in the fork when braking. Even with floating calipers you'd shake at least those around. So a rigid rotor must run very precisely.

A floating rotor OTOH can just adjust itself in the calipers. (It still needs to be turned in tight tolerances, but at least concerning axial runoff it is uncritical.)

That's what I thought.

Thanks once again Markus

They are off a Katana and move maybe a few millimeters, which kinda worries me.  I tried moving the GS rotor and it doesnt budge at all.  Some guy on katriders said they should only move a few micrometers so, I am thinking these are junk and I am kinda pissed.