Its a good habit to get into and to practice until you can do it accurately and fluidly everytime - though i still find it abit hit and miss to rev match precisely to this day. I also do 'heel and toe' in my car as i've been doing it for about 5 years now i can rev match quite accurately without jerking the brakes as i prod the throttle pedal with my heel.

As for small two stroke engines, its not necessary on the road but as i say its a good habit to practice. On the track it only really matters if you're fast enough that during braking you have little or no weight on the rear wheel in which case even the wee engine's inertia is enough to drag the rear tyre and so rev matching is required for added control.

When racing i always felt faster when i was in the first half of the corner, leant over, trail braking but with the clutch fully out and my hand off the lever - with the revs falling as i slowed down, nearing the apex. Its one less thing to think about in that situation and you have more time to feel the engine react as you start to roll the throttle on - maybe just before the apex (though this doesn't apply to every corner) - im imagining Druids at Brands Hatch as i visualise this.
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