You should use the -10db pad when the SPLs are really, really high. And that is the biggest problem with those microphones, IMHO. Which concerts put out sound of that volume that will affect the ability of the microphones to handle such high SPLs? When listening to loud rock concerts, I don't have the ability to judge whether a particular act plays so loudly that they will overload the microphones.
It's a trade-off. Applying the -10db filter can reduce the quality of the recording, but if you don't apply it, you can have a brickwalled recording because the microphone capsules can't handle SPLs above a certain volume. When you place your microphones on a stand 12 feet in the air, it's hard to apply these adjustments to the amplifier bodies on the fly during a show. The only way to really address this problem is to purchase microphones that can handle higher SPLs without the pad. It's one of the main reasons why I eventually sold my Bluelines. They sounded great, but could not handle the high SPLs of some of the shows that I was taping (Oysterhead and the Black Crowes, for example) with the pad off, and I was not about to lower my stand in the middle of a show to apply the pad.
Congratulations on the microphones, however. I really liked the Bluelines a lot. Some tips, as others have said, are to use the ck93 capsules for indoor shows and the ck91 caps for outdoor shows or indoor shows in really nice-sounding places. No, they aren't the most revealing mics in the world, but this can actually work in your favor when taping shows in poor-sounding environments. Also, they're small and have a bunch of capsule options so that's always good.