The advantage of an adjustable rate mortgage is that the rate and monthly payments are usually lower than a fixed rate mortgage. The disadvantage is that the rate can go up if the Treasury bill rate increases, thus suddenly increasing your monthly payment.
Adjustable rate mortgages became more popular in 2004, when the Federal Reserve began raising the Fed Funds rate. This made adustable-rate mortgages more profitable compared to fixed rate mortgages, whose rates are tied to the 10-year Treasury Bond.

