Load team erases any Pokemon you just bought from eggs if you bought the eggs after saving
Yes, sorry if it’s confusing.
SAVE TEAM saves your current team and formation (the Pokémon in your party and how they are arranged on the board) and does so separately for each route.
That means you can have different teams saved for different routes without having to keep making changes in the box all the time.
When you get a new Pokémon from the shop, it doesn’t automatically get added to the current "team saved" unless you do it manually.
I hope I explained that well haha.