Between the various formats like Standard and Commander, theres a lot to keep up with
It stops your opponent from playing spells with even CMCs, and if they control any creatures with even CMCs, then they can't block (and your opponent wouldn't be able to play any more of them anyway)
MTG Modern Horizons 3 Tricky Terrain, Modern Horizons 3 Graveyard Overdrive, MTG Modern Horizons 3 Play Booster, MTG Modern Horizons 3 Play Booster Box, MTG Modern Horizons 3 Collector Booster, MTG Modern Horizons 3 Eldrazi Incursion and MTG Modern Horizons 3 Collector Booster Box Abigail used to be a Tabletop & Merch writer at Gamesradar+ but has now spread her wings as a freelancer
For instance, if you switch Wandering Fumarole's power and toughness, then give it +2/+0 later in the turn, it's a 4/3 creature, not a 6/1 creature