Yes, but you comment out unused variable
once per variable (you can leave those underscores in and clear them out before release). The 2s happens
every time you compile. The badness of slow compiles is non-linear, too. As you start to get to 30s, the likelihood that you check Facebook, Twitter, or hn goes up. At least when you're underscoring unused vars you're doing something
active.
If it gets to 2-5 minutes the likelihood that you stop writing tests and rely on the compiler for bugfreeness goes up - or the likelihood that you create debt by increasing the complexity of your code organization.