Now I'm not saying you need an insert every episode but an occasional song here and there is neat. Insert songs should only be used during a quiet scene with action and not too much talking (I'm looking at you Shura-Iro no Senshi in Z Episode 20). Awesome song but Kaio talking over the whole thing kinda ruined it.
Kai's vocal soundtrack despite being only 15 songs has been really awesome and this time around they used a lot more in the show. Most of them were well placed but some of them but others seemed off and other awesome songs weren't used in the show at all

*Vegeta's Theme, Saiyan Blood, placement was used during a filler power up scene really irked me. I feel that a better placement for this song would be either his Ozaru transformation, his first SSJ transformation (instead of absolute silence

*Trunks' Theme, The Lone Warrior, was during a fight but unfortunately during a losing fight for Trunks which makes the whole thing seem rather off. Perhaps it could have been placed during his first (on-screen) SSJ appearance instead of that weird Jaws-sounding theme or when he kills Cell in his timeline (who knows it could have been but we'll never know now.)
*Kuririn's supposed Theme, Win Tough Fight, wasn't used at all. Supposing it truly is his theme I think the best place to used this is during power up and unleasing of his attack on the Saibaiman after Yamucha dies.
So what are your though on the Kai inserts? Too many songs, just enough, or too little and if you had the choice where would you place them?