In some answer (see there) someone explained that there are several benefits for the two accounts system (one spending account and one reward account). What are those benefits? Wouldn't it be more practical to get your coins directly on your spending account?
For the user, yes, it would be easier to just get your rewards on your spending account as a UTXO. However, this is not scalable at all.
What this means is that every 5 days, the network would be flooded with hundreds of thousands of transactions to pay out everybody's staking rewards. Someday, it would be millions. Sooner than we think... billions.
Instead, the clever researchers and engineers came up with a system of the rewards account. This ada is "virtual" in that it doesn't really exist on chain until it's claimed with a transaction.
They made it so that the rewards values would count toward staked ada so you can continually accrue compounding rewards without having to flood the network with actual rewards transactions. Once you claim it (Yoroi), or create any outgoing transaction (Daedalus), this rewards ada then becomes a utxo on the blockchain and thus non-rewards ada. If you don't need it, it's best to leave it be and only claim when you have to use it. You'll also save transaction fees by not continually claiming your rewards.
Clever, isn't it!