Its called GAAP, or generally accepted accounting principles. Accounting rules stipulate that you match an expense with the benefit you receive. So to use your example of prepaid rent, the business would record the total amount paid to a prepaid account (asset), and expense it over time. With each month that the business received the benefit of occupying the rented space, they would record the pro-rated expense for that month. This type of accounting is known an accrual-based accounting, where revenues and expenses are recorded when they are incurred, not necessarily when the cash is paid out. If a business uses cash basis accounting (as many small business do), then they would record the $6k as an expense on their books at the time the rent is paid.
Accounting wise you have more entries because you have to realize the expenses during the perid incurred. So you can pre pay them but you would see each month the expense being recognized by reducing prepaid rent.
Also paying each month instead of upfront allows for cash flow management, and to hold on to cash to use it for the business as long as possible!
Debit Prepaid Rent $6,000 Credit Cash (initial payment).
Debit Rent Expense $500 Credit Prepaid Rent (each month).
It's called "matching" the expenses to the appropriate time period.
Only for cash flow or budget reporting, to show that income or debt matches the expected budget