OK, I see what you are saying now. You were leveling guns up that you unlock at higher levels, so you wouldn't have to wait until later in the next prestige to start on them to finish the challenges.
This is something similar as to what I do when I know a 2XP weekend is coming up. I get about 5-6 guns and around 10 challenges at the point where I can finish them in a match or 2 and once I prestige and unlock create a class I put the stuff on that I can use and get TONS of XP. Last 2xp weekend I prestiged to 6 and played a game of HCKC and got to level 6, backed out created a few classes with attachements, perks, and guns that were close to finished and wound up being Prestige 6 level 40 in literally about 6-7 matches. I prestiged again at 7 and now am sitting at level 35 (haven't played much this past week) and getting another round of perks/attachements/scorestreaks/guns ready for a mass XP haul.