I am relocating my laundry to a room over my garage. I have an opportunity to put in a floor drain. My old laundry has a floor drain (not sure why -- it is carpet and subfloor with only crawlspace below). Putting in the new drain will not be easy. It requires finding space for the trap and crossing a couple of 2x10 joists (12-OC) with 2 inch pipe. I do not intend to slope the floor towards the drain, but do intend to have Marmoleum or vinyl flooring. Again, it is only garage/shop below. So at worst I would lose drywall and insulation and maybe some tools(!). My previous home did not have a drain in the laundry room, but drains/pans seem to be common practice these days?
Consider that a typical washing machine holds roughly 40 gallons of water. Now imagine that all gushing out onto the floor at the same time. I've never seen this happen because of a washing machine failure, but I have seen it happen when the drain line from the washing machine pulled out and it wasn't a very pretty sight. If you have the opportunity to put in a floor drain, I'd do it - it doesn't add much work, but certainly beats ripping out a garage ceiling to replace wet drywall and insulation.
Another significant risk is from a failure of the filler hoses; they have the potential to dump much more than 40 gallons on the floor.
Even if you always shut off the water supply when the machine is not in use, there is always the risk of failure while the machine is running. The hydraulic shock of the washer's on/off valves could be the last straw for the hoses.
In some jurisdictions, floor drains in a laundry are a requirement of the local building code.
In a related note, is the structure of a "room over my garage" speced for the dynamic load of an out-of-balance washing machine?
From personal experience my husband and I made the mistake of installing a new washing machine in our 2nd floor laundry room without properly placing a pan underneath the machine. We were thinking it was new so there was no chance of it leaking s at least not for a long time. Boy were we wrong! Three days later, a disaster filled the laundry room floor, out into the hallway and started down the stairs. There was something inside the machine that had not been tightened properly. The thought of having to replace our wood floors was horrifying! My husband immediately ordered a drain pan for the washing machine, custom I might add so it works perfect! The company even put a hole in the pan exactly where we needed it to attach to our drain pipe. He purchased it from Killarney Metals. They help take the worry off of us regarding another disaster like that happening again!