Comment by judofyr

The point is that Wave is never going to replace email over the night, so in the beginning it's very useful to get an email whenever something interesting happens. As you receive more and more emails, you realize that it's a lot easier to just keep Wave constantly open and you'll turn off email notification.

But before that point Wave does not deserve its own tab, and because of the lack of email notifications it's very easy to simply forget about checking Wave.