I disagree, I absolutely think you should go in with a reasonable amount that you would like and to explain it to your boss.
I have done this both ways in the past. When I didn't specify, I got less than I had hoped, and when I asked, I got exactly what I wanted. The most awkward conversation would be asking for a raise, then asking for more because you didn't specify.
If the boss can't afford what you want or doesn't agree you deserve it, its his job and within his right to tell you no, or what he is willing to offer you instead.
If you prepare yourself ahead of time, explain why you deserve a raise, and how much you would like, you have a higher chance of getting it. That way, you don't have to wonder what would have happened, had you just mentioned what you wanted.