Heeling & toeing comes from the bad old days of non-synchro manual gearboxes, where you had to double-declutch in order to engage a lower gear. There's no actual "need" to do it now, but it does help the gearbox synchromesh along a bit, and it does make deceleration smoother by matching engine revs to road speed, so you don't get that lurch when you engage a low gear and release the clutch. And it's fun. ;-)

Here's what you do. You're in 4th gear at 75mph, approaching a 30mph bend. To slingshot out of the bend, you want to be in 2nd gear. So you start to brake. As you brake with the ball of the right foot, you angle your foot over so you can work the throttle with the heel of the right foot. De-clutch, move the gearstick and blip the throttle all at the same time, so the gear goes in nicely and the engine revs are nicely matched to 3rd gear road speed. Then do the same for 2nd. By this time you're smoothly in 2nd at 3K rpm, ready to plant your foot out of the corner.

But you can only do it in cars with the right pedal heights, etc ... And S/V40s don't have it (at least not for my size 10 Doc Martens)