Here's a fun scenario from my ELEAGUE match against Seth Manfield last night where I played Keruga Jeskai Fires and he played Lurrus Rakdos Sacrifice. I had this approach planned out once I saw his decklist, and just checked the VOD to discover it played out like I had hoped;

I didn't board in Grafdigger's Cage in game 2 of our match because decklists were open. He knows I have 3 Cages in my sideboard (which he'll likely assume I'll board in), and I know he has 3 Shieldbreakers in his sideboard (which he's going to board in to answer Cage).

As soon as game 2 starts he sees that Keruga is my companion still, and immediately knows that I don't have Cage in my deck in game 2 due to Keruga's companion restriction. This means the Shieldbreakers that are now in his deck are incredibly low power level.

When we go to sideboarding for game 3 I remove my companion so that I can sideboard in all 3 Cages, whilst he takes out all his Shieldbreakers having seen (via my Keruga) that I didn't have Cages in for game 2. This means I get to have Cages in my deck vs no Shieldbreakers.

Thought this whole scenario was really cool, and feel proud that it worked out exactly like I'd hoped when I planned it out ^_^