alright, think of it like this; optimizing your movement is crucial for map control. how, and why?
you want to get to where you need to be fast, so that you can save time for doing it again. for example, if you see someone taking an area such as north or south in saltspray by coating it in their ink, you need to get there as fast as possible, so that when you reclaim it, you'll have time to reclaim the next area that's been taken, like square or snakes. if you can outmaneuver the other players, you can deny that area from them and keep it for yourself. in addition to having knowledge and skill in dm and positioning, movement is a crucial skill in shooters, but especially splatoon. if you were to just superjump to that area, that telegraphs your position to the other team and you don't cover ink along the way. if you were to just walk there or do something more basic, well that works too, but it's wasting time. let's say that if you s-hop and sdash from spawn to mid and make it there in 10 seconds, and walking there takes 20, that's 10 seconds saved. you can frag probably the entire other team in that time span, they'll respawn in around 4 to 5 seconds, and take another 10 or 20 seconds to get back to where they were, to give you an idea on how major that is. the more time you save, the more time you have to coat the map in your ink without hindrance. this is why techniques like rocketjumping in games like quake and tf2 are so emphasized; optimizing your movement is optimizing your time, and optimizing your time is optimizing your game.
will these techs be useful in the long run? we'll have to see, yeah, and i'm not going to put all my eggs in this one basket. but it's just absurd to look at this and say "hm... no. that's not very useful," especially considering how applicable these techniques are. you can s-hop and sdash literally around the entire map, and at any given time. you can use it to get out of a fight gone wrong, and you can use it to rollout to mid, you can use it as a shortcut through areas, etc...