It's unsure how interest rates will move at any given time, but your lender may estimate where interest rates are headed. If interest rates are expected to be volatile in the near future, considering locking your interest rate may be good because it allows you to qualify for the loan. Or, if your budget could handle a higher loan payment, or lender's lock fees, you may want to let interest rates "float" until the loan closing.
*All rates are subject to approval with 80% loan to value, 740 fico and Fannie Mae, Freddie Mac and FHA loan limits apply.