The styrofoam can help level out an uneven surface, like foam on a mattress. If you get a corner on a high spot, it puts stresses on the glass, and can cause failures. I had this happen with a 30 gallon tank of mine, it was a MESS.
If you set the tank, empty, on a surface, and can see light under it at any point, you've got potential for stress fractures and corner leaks.
didnt know that. I have a question though. It seems my fish will do fine for a few days then one dies then two etc etc. Is there a reason for this or is it just because its a new tank maybe has to be "broken in"?
The styrofoam is a very good idea. With a homemade stand, if you ever had fractures in the glass you could forget about getting reimbursed from the manufacturer for a failure. With a larger tank it would be even more important to make sure you had a suitable stand and used the styrofoam sheet. My brother has a 125-gallon reef tank and built the stand for it. With more than 1000 lbs of weight on it he had to make it beefy. It was also tricky getting the stand level on his uneven floor. He took some risks but he hasn't had any problems. If he did though, he'd be screwed and wouldn't get compensated for a manufacturer defect.