It prevents multiple "impact" defensive signings, which was my point all along. The few times the Pats have stretched for big names (Colvin, Thomas) they did so without a franchise tag* on their cap. As we both know, they rarely spend within ~$5M of the ceiling - whether the changes to NLTBE bonuses changes that core philosophy is to be determined.
But ultimately, you are correct - tagging Welker should not prohibit them from one "impact" signing. If that signing is another WR, I'll be pissed; it's too much $ to spend on one position. (IOW, Mike Williams & Vincent Jackson are no longer options)
*Was Vinateiri tagged in 2003 or 2004 for the first time? Either way, they tagged a kicker, not a player with a consequential salary.
Why would or should you be pissed? There's reason to believe that the Pats offense is missing one piece -- an outside, fast WR. Sure, when everyone is healthy, they were able to prosper. But if any of Welker, Hernandez or Gronk is dinged, the lack of someone on the outside is problematic. We saw that in the SB and we saw that in the Jets playoff game, when Aaron wasn't himself. (Yes, I know, different teams/years, but a common link is that the Pats offense in both playoff losses did not have all of its key receiving parts in good health).
Sure, the Pats have big needs on D, but they have many high picks and have shown an ability to find cheap yet effective free agents for the D. And their expensive free agents on D in the past have not always panned out (though Colvin did perform well at times).
My point is that no free agent signing in isolation should piss you off. If the Pats decide to augment the receiving group with a big name free agent like Wallace (or better, somone one who doesn't cost a pick), we should only be upset if the sum total of their other moves this off season doesn't adequately address the defense. And the opposite is also true. If the Pats don't address the need (in my view) for an outside WR threat in high end free agency, we should only gnash our teeth over that if they don't spend the money on other needs and otherwise fill in at WR.