This is a really nice trick for many 2WD cars which don't have droop tabs, but most 4WD cars already include this tuning option, so be sure to only go this route as a last resort. I also favor using plastic spacers instead of cutting fuel tubing because it's difficult to cut perfectly equal lengths which is very important for consistency. In contrast, most of my car setups have me extending my droop by backing out the shock ball ends a few turns.

Traction roll is typically mitigated with ride height, which was listed as the #1 priority adjustment in the chart I linked earlier. These guys should start with a good baseline setup before blindly making any other tuning changes, they could have their cars so far out of whack they could easily create bigger problems elsewhere. It's better to start in the center of the tuning window rather than in a far corner which will drastically limit your options