haha..... "combo guard" is just a euphemism for a short shooting guard who has little to no point guard skills.
However, when said combo guard is further down the rotation, he can be an asset. Question would you rather have 3 pure PG's and 3 pure SG's (6 total players).....or 2 pure PG's, 2 pure SG's, and a combo guard (5 total players)?
Totally dependent on skill level and skill-sets of the players involved. In general though, I think 6 guards (regardless of being a 1 or a 2) is probably 1 too many for a roster -- the Blazers have 6 right now and could have up to 8 assuming they keep both Armon and Mills.