Ok, I’ll use V-Sakura as an example, because hers is most commonly used.
Sakura’s normal B&B VC consists of activating VC2, launching the opponent with dp+JP, juggling the opponent with back+FP, then whiffing either her qcb+SK (midscreen). Or in corner, juggle with FP and whiff her qcf+P.
In other words: (VC2), DP+JP, [b+HP, whiff QCB+SK]xN – untill corner
- corner: [HP, whiff QCF+P]xN – untill about 20% meter
However, using walk cancelling, Sakura is able to tack on about 5 j.FP’s at the end of her VC, followed by a c.FP xx dp+RK > Px3.
To do this, most players will whiff one last final qcb+SK, and cancel it into a whiffed standing SP, then immediately hit with jumping back SP (7SP). They do this because Sakura can’t simply jump up and hit the opponent without reaching a neutral state (allowing the opponent to tech flip). Whiffing the standing SP ensures that Sakura is not in a neutral state (because she is attacking), untill her shadow hits the opponent. She then recovers from the SP right as her shadow hits her opponent. However, the opponent has a very very brief ammount of time before the j.SP hits them. In fact, if timed perfectly, the opponent only has about 6-11 frames to tech before the j.SP connects.
While Sakura is landing from her jump, the opponent is hit again with her shadow (the shadow of the j.SP) and is launched rather high into the air. If she crouch cancels and attempts to hit the opponent again, anything she does will whiff. She can’t just stand there, and if she jump cancels twice, her opponent will be far too low to the ground.
This is where walk cancelling comes in. Once she has landed from the j.SP, she can begin to walk cancel toward the corner. Her crouch cancels the jump recovery, and the walk cancels the crouch animation. While walking, the opponent can not tech flip (because walking isn’t neutral).
She can then cancel her walk animation with a jump any time she pleases. She only needs to walk a very short distance (about the range of a c.FK) before she can jump and hit the opponent with a FP, but that little bit of time makes all the difference in the world.
She can then end the VC with about 5 CC’d j.FP’s, then c.FP xx dp+RK > [P]x3
Which refills about half of her meter.
Other characters, like Karin, can make similar uses out of walk cancelling.