I'd imagine he'll effectively take snaps from Irving and Trevathan as the #2 nickel LB when we move Miller to a pass rush position. It'll be a good role for him.
He'll need to earn a larger role either by outplaying Woodyard in those situations when both are on the field, or by proving that he could replace Brooking at MLB.
He adds depth and will help shore up our nickel unit against short to intermediate passes over the middle of the field (still our biggest weak spot). Should be a useful addition at this point in the season.
Doesn't change that the FO needs to be thinking about cutting him this off-season and replacing him with a younger, more responsible LB.