I've never had a problem with digging in. I do quite a fast side-to-side lay onto my jigmaster under a bit of tension. But I also don't load my grinders under too much pressure. Grinders don't have the gearbox ratings that multipliers do. A multiplier on a boat rod filled with mono is designed to "winch" in a fish. Grinders on the other hand, require pumping... taking up slack with the reel as you pump the rod, simply because the transfer of energy into the rotor arm is not efficient like the transfer of energy from the handle into the spool of a multiplier. Gear ratios do come into it, but by and large, grinders should not be asked to do a winching job.
The first throw of a plug, popper or a stick bait without a hookup will always result in very low tension take up, so when loading new braid even your last 100m or you could do under a very small amount of tension, thereby saving your gearbox a little wear and tear. I do however feel that the first 1/3rd or so should be as tight as you can.
I'm always a bit concerned about my gearboxes when loading braid (and I only use high end reels).