It's a low risk move to be sure, but do the Pens need more gritty players? Here's a list of the potential third and fourth line players on the roster right now (and I'm assuming Staal and Dupuis are in your top 6, given the lack of other options currently):
Cooke, Rupp, Talbot, Adams, Kennedy, Asham, Godard
I guess the question is, do you want Asham filling a temporary role in Pittsburgh for a year, or would you rather see someone like Tim Wallace or Dustin Jeffrey getting an extended look on the roster? This signing might say more about the lack of confidence in some of the young guys than anything else.
Maybe given the potential changes on the third line, Shero sees the value in adding a responsible forward that can play either wing and occasionally chip in on offense.