The move clears space on the 40-man roster:
Before jumping to conclusions and saying your goodbyes to the righty, consider this: Atchison is a soon-to-be 30 year old relief pitcher who's collected a total of just 37.1 Major League innings over his career. His minor league track record is unimpressive, he hasn't consistently pitched out of a rotation for more than three years, and he spent most of 2005 sidelined with an elbow injury. This is a guy who shouldn't have too much of a problem clearing waivers and going back to Tacoma, where he'll wait for a member of the Mariner bullpen to get injured so that he can get another crack at the AL.
And hey, even if he gets claimed, it's no big deal. Atchison isn't going to keep striking out 11 batters per nine innings in the Majors, and at 30 years old, he's already as good as he's ever going to be. Which isn't to say that he isn't useful, since he's perfectly capable of providing 1+ innings of effective relief every other day or so, but he's pretty easy to replace, because every organization has a bunch of guys like this, including the Mariners. If he makes it through waivers, neat, you have Scott Atchison in AAA. And if he doesn't, whatever, then you just bring in the same kind of player from somewhere else, be it Tacoma, Kansas City, or Japan. The bottom line is that, while some of these guys can be worth a lot of money (like George Sherrill), most of them aren't, and letting yourself get too attached to them is unlikely to turn out well.