thats kind of an odd question. theres only a few specific uses for wavedashes, but overall its seen as more of a movement option than a purpose-specific tool. this is true across the board for every character (minus some of the big wavedash characters i guess)
the wavedash is a 14-frame scooting movement (4 frames jumpsquat, 10 frames sliding [longer for characters with longer jumpsquats]). it allows you to reset from any jump-cancellable position into a neutral standing position while giving you the option for movement throughout its duration. this is big, because many jump-cancellable positions dont generally allow you to reset to neutral stance while offering movement simultaneously. jump-cancellable positions for pikachu include standing, walking, initial dash, run, and shield. (also 2nd half of taunt lol) im gonna go over how wavedash applies to each.
- standing: this IS neutral stance. this is the position you enter out of wavedash. however, this doesn't mean wavedashing from standing is useless - the only other movement out of standing that is equivalent in movement speed to your wavedash is your initial dash, but initial dash takes longer to end unless you dashdance back (in which case you'll have to wait for the new iteration of initial dash to end...you get where im going with this).
- walking: this is similar to neutral stance in that most of the actions you can do in standing are also offered during your walk. again, wavedash during walking operates similarly to how it works in your neutral stance, except walking offers you the option for movement while keeping your neutral stance options the entire time.
- initial dash: when you enter run, your first few frames are your initial dash animation. during this animation, you are given the option to dash backwards immediately (when several are done in succession it is known as the dashdance) but lose the ability to crouch or stop the animation (it must play to the end). in this case, wavedashing is a great way to exit out of your initial dash or dashdance early - you still commit some frames to lag but you enter neutral stance more reliably and maintained controlled movement (rather than initial dash's awkward deceleration).
- run: this is your normal run animation, which is if you hold the control stick after your initial dash. you lose the option to dash backwards immediately (you perform an awkward slide instead) but regain the option to crouch and have a faster stopping animation (which is negligible since you can crouch stop your run). wavedashing out of run is useful if you want to reverse your momentum faster, or you want to enter standing/walking in the same direction earlier without having to crouch midway.
- shield: this one is big. generally, shield offers you 5 options: 2 roll directions, jump, spotdodge, and drop shield. however, the jump option gives you a lot to work with considering how many jump-cancellable actions there are in the game. of these options, wavedash is the only one that offers you a quick movement option that ends in neutral stance.
as for specific uses...
(wd = wavedash, dd = dashdance, oos = out of shield)
one big way pikas use wd is counterattacking oos (more so than many other chars imo). that is, approach with shield > shield opponent attack > wd > punish. its a pretty strong mixup if you conditioned the opponent to zone out your approaches. particularly strong vs marth. watch axe vs any marth for this lol
mixing in wd's into your dd is pretty common, but you need to know when and why to use it during your dd (doing all your movements with purpose). i suggest developing your dd game first before mixing in wd's. a lot of what pika does with wd in dd is kind of like...confusing the opponent. the most common one that everyone brings up is the run up > wd back bait, but you can do a bunch of movement oddities with wd. the idea is to shift your position and movement around enough to confuse the opponent, making it harder for them to read your approaches and such. theres more to it than this, but you just have to experiment with dd'ing to see what i mean
wd onto ledge is good but pikas often use the upb to get to the ledge faster
one particular way i like using wd is during edgeguarding spacies. i run towards the ledge and wd towards the ledge but not to the point where i touch it. this way i can do my ftilt faster than if i were to wait for my run to end, plus i already buffered my forward input during my wd (just hold forward during wavedash) also works with crouch i guess, but i prefer wd ftilt
theres a bunch of other stuff. but the most important part is in the first half. keep playing around with wd and you'll find uses for it on your own
as for videos...find any axe video and identify the wavedashes i guess <_< im lazy when it comes to finding examples lol
really really late edit:
i also want to add that wavedashing is the only way to move backwards, giving interesting ways to control which way you face
well, moonwalking exists but moonwalking sucks lol