There's almost no excuse not to use Scala if you're deploying on the JVM.
Lots of garbage generation. I like Scala a lot, but the space where I can really use it is smaller than I'd like. I do really like it and Play for one-offs, though.
In practice, we have seen much much _less_ garbage created by our Scala code. The use of objects in Scala encourages static method creation, and there's so much boilerplate Java junk that your Scala code just doesn't need.
Lots of garbage generation. I like Scala a lot, but the space where I can really use it is smaller than I'd like. I do really like it and Play for one-offs, though.