I find this to be a must have in your arsenal and not just for decon. I use it to spot treat things like tar or sap. I also use this to remove emblems or other adhesives. In the decontamination process, I'd use this in combination with clay or AutoScrub to get those areas behind the front and back tire where tar and other heavier stuff tends to build up.
A couple of things to note: you don't want to let this dry on anything plastic or rubber. It will stain it. You also wouldn't spray an entire panel with this. You'd use it sparingly directly on a spot. This 1L bottle is probably going to last you a few years.
You could watch the video above if you'd like, but I use this like so. This is the second step of the decon process.
Use before or after clay/Autoscrub. I tend to use it after paint is decontaminated.
Spray on spot.
Let sit for 30 seconds or so. I tend to wipe or catch the runs underneath the area that I just sprayed.
Then proceed to wiping and respraying Tar X until the spot or adhesive is gone.