Biggest downfall to a stainless table top is that spatter will stick much more readily to the surface. Getting spatter off a stainless surface usually requires a grinder/sander, it typically won't knock off with a chipping hammer or chisel. Since you got the piece of stainless for free, maybe put it away somewhere and pull it out if you are going to be welding stainless. Using the stainless top in those cases will save your parts from picking up carbon from the table top.