If you are in a stormy part of the country, and want to leave the alert capability turned on, S.A.M.E. is worth the money and the effort to program it. Some weather radios plug into the wall. Check to see if they also have battery backup. A weather radio that doesn't work during a power failure is pretty useless. All of my AC powered radios have battery backup power.
Some radios only run on batteries.
If you leave those on in alert mode too long, the batteries will die. They should not be considered for long term alert monitoring. Some portables can run on both, but may not come with an AC supply. If you may ever want to take it with to work, on vacation, or just to another room, you may want to get a portable and just leave it plugged in on the nightstand most of the time. Some portables are also weather resistant, for boating, camping, hiking etc.