It depends how strong it is. The obvious benefit for a malicious person would be to set their meter to the cheaper tariff by replaying the signal. It wouldn't

It depends how strong it is. The obvious benefit for a malicious person would be to set their meter to the cheaper tariff by replaying the signal. It wouldn't need to be a powerful signal - if you were broadcasting right next to the meter even a few milliwatts would be enough. Build a faraday cage around the meter to be sure! Just remember to dismantle it before the meter reader comes round.