Rotom-W makes such a great candidate for that lead position because of its coverage and unpredictability off the bat (the latter is significantly reduced after that first turn once you can make an educated guess at what set it is running). Volt Switch lets you scout and do some nice stab damage - which ground types won't usually try to block in fear of being drowned by a HydroPump. Once you see the Volt Switch it would not be unwise to assume they are running specs or scarf (but then you have to guess which one before risking being revenged later in the game).
Unfortunately, the bloody washing machine also has the ungodly ability to spread burns, crippling switch ins to its high powered attacks from the first turn of the game if you incorrectly predict a choiced variant.
On top of all that, it is bulky enough to take a hit or two.
Man, I despise that thing.