Why is it important that maglev trains do not touch their track?

I'm not too sure about the advanced physics of this, but I know that it is desired for Maglev trains to not touch the track so that their speed can be maximised, and so there is no wear and tear of the track and contact.

The speed would be maximised because if you don't touch the track there is no friction. Even wheels are slowed by friction so the only way to completely eliminate it is to have no friction.