We have been using spray foam in our bathroom and home renovations for coming on 6 years now. This spray foam product really is the bomb and if you can afford it will be well pleased with the money spent.
We have done barrel dormers, crawl spaces, sub floors, exterior walls, roofs and everything in between.
In my own home renovation I choose to use spray foam in about 2/3 of the home and we are amazed with how quiet or home is and how little the demand for heat is.
With bathroom renovations and wanting to place fixtures on an exterior wall it is possible to meet code restrictions with just 2"x4" wall framing. This little space saving can help with fixture placements - perhaps not a mixing valve or thermostatic cartridge but a wing back or flow valve should fit nicely. Most times pipes freeze because of air movement over a cold pipe. When you take the air movement away things really stay warm.
Also when a bathroom or kitchen is not over a heated space the spray foam on the bottom side can really keep a floor warm underfoot. We sprayed out a 10'x10' area beneath my wife's kitchen and this part of the kitchen floor never feels cold.
Now you can also choose a 1/2 pound foam for just sound and the regular I think 2 pound foam for insulations. I noticed on my spray foamers business card there is even tax rebates you can qualify for if you follow all the right steps.
Who else is working with Spray Foam?