Personally although ATM my 55g is more of a holding tank over a grow out, as i plan ong buying a 200g or building one, I do plan on using it as a grow out later as i do tend to gravitate to more aggressive & Larger species for my tank for smaller less agressive fish i have a 2nd 55g, as well as a breeding 30g tank.
As far as agreeing with it, i do, because like another posted if your tank has already matured you really risk new fish, and if you don't have a quarautine(sp?) tank then it can be used as that if your new fish are only ones in there.