I have noticed that some banks offer short term CDs with interest rates that are actually lower than that that the same bank pays on a savings account.
For example Ally bank seems to offer a 0.30% APY for a 3 month CD (up to 0.39% if you deposit $25,000 or more) while their online savings account is offering a 1.05% APY.
What reasons would there be for purchasing such a CD instead of simply parking the money in a savings account?