The Chargers front office was feeling like the offense was a bit TE-heavy, so they wanted to balance things out with another Wide Receiver. Roscoe Parrish is the latest free agent to be added to the team, on a one-year deal and it appears he's coming on board as mostly a special-teamer.
You might remember Roscoe Parrish as a member of the Buffalo Bills. There, he fulfilled mostly Punt Return duties, with some Kickoff Returns and work as a Wide Receiver. He comes to the Chargers having only played 10 games in the last two seasons. He went on IR in 2010 after 8 games with a broken wrist; then again after 2 games in 2011 with a pesky ankle sprain. After his most recent stint on IR, Parrish became expendable following the emergence of David Nelson.
With Eddie Royal and Richard Goodman on the team already, adding Parrish now gives the Chargers three Wide Receiver–Kick Returners. At this point, it appears Eddie Royal has the job, leaving Parrish and Goodman to fight over the remaining spot. I have to imagine whichever of those two has the better preseason stays.
This looks like a nice low-risk move for the team, and buys them some insurance should the team suffer injuries at WR, KR, or PR. However, he may not be the best insurance policy against injury considering his fragility lately. Who knows, maybe he's moved on from that chapter in his life.