Placing a desktop vertically

We use IBM 300 PL desktop PC’s in our Call Center and have several of them placed vertically to give more space in the work areas. I was told by a supposed higher up that it was not good to do this to a desktop model. However, these particular models have a vertical switch built in the cd rom drive. I have read the manual to the model mentioned, and it doesn’t contraindicate otherwise. Actually, it gives instructions on playing CD’s with the CPU in the vertical position. Can anyone give mea truly valid reason why this shouldn’t be done? I want several opinions and wish to divide the points among opinions given. Thanks in advance………..Techie Girl