Each half of the LP pair will always have equal USD value. Both added up equal your total USD investment in that farm.

Your USD investment value into the farm grows over time, because of the Liquidity Provider Fee, that people have to pay for every exchange of two tokens, when using the Cub Finance exchange. When they trade using tokens from your liquidity pool, for example when selling CUB into BUSD, the fees will be shared with everyone in that farm. You find that info on the exchange page in the info box below.

For each trade a 0.2% fee is paid. 0.17% goes to liquidity providers and 0.03% goes to the PancakeSwap treasury.