When the borrower decides to keep the interest rate fixed for the entire period of loaning, it is known as a fixed-rate interest. As a result, the monthly payment remains the same or amortized irrespective of the time period.
It proves beneficial in volatile markets where interest rate in the housing sector fluctuates frequently. However, in case very long-term loans, say 30 years, it might turn out to be expensive only if the interest rate drops.