Sarcasm aside, Holiday, who played for the Broncos last year, makes sense because he has experience playing in a 3-4 scheme, which the Redskins are switching to this season, or so I've heard.
It's impossible to ignore the elephant in the room here - the Albert Haynesworth situation. The Washington Post's Rick Maese writes that Holiday gives the team "plenty of options" as they "figure out how the Haynesworth situation will resolve itself." SB Nation's Redskins blog Hogs Haven notes that Holiday is most comfortable playing the same position Haynesworth is slotted to play.
Although Vonnie only started 3 games, he saw a lot of action and played well as the right defensive end. This makes for an interesting scenario since Haynesworth was slotted to be the RDE with Jeremy Jarmon as his backup. On the left side it's Phillip Daniels with Carriker backing him up. I can't say this really adds pressure to Albert since he already got paid, but it does give me the notion the Redskins are making a contingency plan.