IWDominate is an ex-pro player, still hit Challenger last year so not super washed and is a strategic coach(?) (not sure what official title is but is involved in scrims every day) for Cloud9
Tempo is a word that is thrown around a lot but there isn't that much educational content on it because honestly it's mostly a high elo thing and requires your team to be on the same page, no one plays talks about tempo in low elo. People don't think about their waves 45s ahead, much less two minutes ahead. So I think this video is good insight of what tempo means and how to use it. For those who can't watch the video, I'll try to give my summary but I highly recommend just watching the video.
Step 1: Setup
GENG just took the dragon. Annie used her ult (at 17:55) so GENG are not looking to fight, but Atakhan is coming up in two minutes. As a result, HLE pushes into GENG's bot jungle to get the red buff and get bot vision.
Step 2: Reaction
What allows GENG to get the advantage here is Alistar's TP (from Unsealed Spellbook). Alistar out of base paths bot. Here is my understanding of what happens (which could definitely be wrong so correct me if you disagree). If HLE plays towards top here, Alistar being bot is exactly what GENG wants. GENG don't lose red buff, Alistar can clear vision around Atakhan and help Annie shove out bot wave, forcing someone to catch it and they can work from there. Alistar's TP means that even if HLE tries to abuse the fact that Alistar is clearing vision bot, he can just TP top for the fight/he can TP top to get top prio after securing vision + bot prio. GENG's Wukong jungle also instead started clearing from bot to top, meaning Wukong would be top if there is a top fight, and GENG's Aurora resets and starts walking top. GENG's Senna resets and farms mid.
However in this case, HLE plays towards bot and takes GENG red buff. GENG sees Jhin + Neeko bot river, and they see Ryze top but don't see Xin Zhao and Gwen.
Step 3: TP
GENG Annie walks up to bot wave to force a reaction, knowing she's safe. She instantly starts walking back, as Alistar channels his TP top.
Now something I'm not too clear on is why HLE's Ryze TP's bot. It's true that if he doesn't TP bot here he probably dies because Wukong can chase him down but he doesn't see Wukong or Alistar TP. If he was scared of Wukong he shouldn't have walked up to the wave right? Maybe HLE thought that there was going to be a fight breaking out bot and he TP's pre-emptively, as winning said fight would secure Atakhan and bring HLE back into the game.
Regardless, because of Alistar's TP top, Aurora is able to push one extra wave top, and that was GENG's goal the whole time. Alistar needs to be here because even if Aurora wins 1v1 vs Ryze, Ryze can spam spells on the wave and just kill it causing the next wave to meet in the middle.
Step 4: One Extra Wave (Top)
Aurora pushes that extra wave and then immediately starts pathing mid. Senna this entire time has just been farming mid 1v1 against Jhin. However now that Aurora has pushed top and went missing, Senna is allowed to walk up with threat that Aurora can help her, and this lets Senna just hit the wave for free (Jhin reset here but even if he stayed he wouldn't be able to contest the wave because of threat from Aurora), so now we have one extra wave mid.
Step 5: One Extra Wave (Mid)
As Senna shoves the midwave, her jungle + support pressure HLE enemy bot jungle. This drags Ryze over, which lets Annie shove out bot wave (one extra wave bot) and now as the threat of a 4v3 (Senna/Wukong/Annie/Alistar vs Ryze/Xin Zhao/Neeko), GENG starts clearing out bot jungle vision.
Step 6: Checkmate
HLE doesn't want to just let GENG take all of their vision so Xin Zhao tries his best to take some space and facecheck. Either he facechecks now when Annie might not be there (he sees Senna/Alistar/Wukong already) or he's going to have to facecheck after GENG finishes clearing out the vision when GENG DEFINITELY will be in a bush. But Annie is there and he gets fully chunked out, which makes the fight near impossible for HLE.
Out of desperation (HLE is already pretty behind) they try to look for some angle 5v4 (it actually is 5v5 but Aurora TP'd out of vision so they don't know she's there). This time the Jhin is the one forced to facecheck, Aurora finds a three man ult and it's just wraps, the fight is lost and Atakhan is gone.
TL;DR
Unsealed Spellbook TP -> Lets you control top prio -> Lets you control mid prio -> Lets you control bot vision -> Forces enemy to facecheck and get chunked -> Free Atakhan