[Arelius]

Constand delta time does not solve collisions. You should always be using continious collision detection for things you care about, or eventually something will go to fast even for fixed dT.

One good argument for variable dT is if you do enough logic such that game time may be a major performance bound. If on a machine that is running fixed dT cannot perform all computation in the allotted time, then the game will get behind schedule, and how do you resolve the problem of having a wall clock 10, 100, or more frames ahead of simulated time when you can't keep up. In that regard variable dT degrades more gracefully.