If you have to do any travel for work, a lightweight but fast portable machine that is easy to lug around beats any productivity gains from two machines (one much faster) due to the challenge of keeping two devices in sync.

Having a backup system can be kind of priceless sometimes. Also, if you have a desktop and a laptop you probably use one of them 80-90% of the time, so you rarely loose time syncing stuff.

I do this regularly and it's really not a big concern.