When it comes to the starting five you get a chance to really impact the talent level of the team. When it comes to the bench your into a balancing act. A pure SF who could shoot, but didn't have the handle Daniels has - would have forced the C's to pickup a backup PG. Daniels allows House to play more minutes. I'm not sure the C's will be able to add a PG that provides more talent than House. Having Posey as the backup wing, would be a better fit with a guard more like Marbury's skill set off the bench, rather than House. That made more sense two years ago when Rondo still had question marks.
C's have the following guys to play both guard spots and SF (in order of expected MPG) - Rondo, Pierce, Allen, Daniels, House. Everyone, but House has good handle for their position and 3/5 are good 3pt shooters. Four big men are likely to get minutes Perk, KG, Sheed, and Scal. Both guys off the bench are good 3pt shooters, and KG has a good outside game. All are above average ball handlers. I think offensively the team has a good enough blend of skills to make things work. I do wonder if Daniels will see a jump in defensive ability like Ray Allen and Eddie House in the C's system and under Thibs. If he's able to play the other teams better wing while in off the bench this is a great signing. If Pierce (or Allen) retain that responsibility it's probably just a good one.
In terms of filling out the backup PG spot - if Pruitt goes, they need a guy who is capable enough starting for a few games in case of a Rondo minor injury, but not going to complain riding the pine. They don't need someone who plays ten minutes a night. If Rondo goes down with something serious (a la Jameer Nelson) Danny will have to find a replacement on the fly.