+1 on Dan's comment about getting hss too hot to ruin the steel. Pretty easy to do on old carbon steel tools but today's steels are pretty tough to get that hot. You're more likely to ruin the cutting edge by mis-grinding than by overheating the steel.
However, with that said, I use white friable wheels on a slow speed grinder and keep a cup of water handy. Mainly because I can control the grind so much better and I can touch the edge after a dip in the water.