According to the Boston Globe's Ben Volin, the Patriots are making four moves today.
Grissom spent the season in the injured reserve and was projected to have a Kyle Love-type role in 2014. It's apparent that he was more destined to be like Marcus Forston. Similar to Moe, the Patriots must've felt that his recovery didn't leave him in a desirable position and that his roster spot could be easily replaced.
McGuffie was brought aboard to play the role of C.J. Spiller during the season and stuck around as a prospect with tremendous athlete. It's likely he's more of an athlete than a piece the Patriots could utilize on the team.
Reed was a depth addition and is considered fungible.
None of these moves should be related to cap space and most are likely done to allow the players to sign elsewhere.
EDIT: Field Yates has announced three more releases. RB Quentin Hines, OL Elvis Fisher, and OT Brice Schwab. All three were released from the IR and were camp bodies this past off-season.
The Patriots are currently using 59 out of the maximum 90 roster spots.