What does the exp actually do?

Interesting how tricky it was to find the answer to this but I discovered that EXP helps increase a company's level (indicated by the money signs under its name) which in turn helps you get a larger amount of rent from them.

Answer found at https://www.mrguider.org/strategy/idle-office-tycoon-cheats-tips-strategy-guide/#idleofficetycoonexp

EXP will help you gain levels, that will then unlock new areas in the game. You can see your current level in the top left of the screen.

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