Do not unplug the resistor - unless you like jerky deceleration.
The shift kit allows you to tune the how quick (firm) the tranny shifts. If you are happy with your shifts, then no need to buy one. Many people including myself have found the 2-3 shift verrry lazzzzy. The shift kit will make that shift much firmer.
The early shift kits caused the power light to blink unless you added a resistor. They also had 3 prongs and only 2 were used. Installation instructions that (at best) were incomplete, led a few people to hook up the kits incorrectly. From what I hear the new kits do not cause the power light to blink and with only 2 prongs, it would be hard to hook them up wrong. So So if you feel you would benefit from firmer shifting then the kit is a pretty cheap way to do that.
-Matt