For me Heel and Toeing is complete overkill for my everyday driving.
Rev-matching is a must for car like S2000 which relies on your behalf to downshift frequently. Say you are cruising 70mph at 6th gear and have a sudden urge to reach the 100mph+ fast. Your choice of gear to complete the task is 3rd. Without the rev-matching and downshift from 6th to 3rd(if you can) you will lurch and jerk your car like you wouldn't believe. For a smooth and correct transition would be clutch in and while passing the neutral blip correct amount of the throttle to raise the rpm and shift into the right gear and release clutch.
Skipping that much gear quickly isn't easy and I occasionaly mis-shift myself but easy way to practice the rev-matching would be going down sequentially from 6-5-4-3-2 and ultimately 1.