Is that bit in The Queen’s Gambit about chess players coaching each other between matches complete bullshit? Or should one expect a player to occasionally play uncharacteristically when the stakes are high because they would seek out advice which skews their play?
Also psychological games fall neatly into the scenario you describe. I play better and you play worse because I got into your head, or sent the noisy people to be across the hall from you instead of from me, so I slept like a baby and you didn’t.
The adjournments in The Queen's Gambit were rendered obsolete after chess engines became strong enough to be useful in analysis. The last year that they were permitted was 1996.
Match play at the World Championship (where the two players play each other repeatedly for many games) involves a ton of inter-game coaching and work as each player's team goes over what went well, what went wrong, and how the next game should be approached.
Round robin play in small fields also has a significant amount of preparation because the schedule is known in advance, so players will know whom they have to play the following morning and will prepare accordingly.
I'm not comfortable saying that Hikaru does exactly 0 preparation for 3-minute Chess.com blitz games, but it's probably pretty close to 0.
Also psychological games fall neatly into the scenario you describe. I play better and you play worse because I got into your head, or sent the noisy people to be across the hall from you instead of from me, so I slept like a baby and you didn’t.