Depends on whether you get good cell service throughout the lake. Depends on if other boaters use/monitor their VHF. Depends on if there is a law enforcement agency that patrols the lake.
Having one isn’t a bad idea at all, you may be surprised at how many folks actually monitor. Also the Sherriff’s Department and DPS monitor on most of the lakes, especially on the weekends during the season, so if you have an emergency, need to report something, it can come in handy…what lakes in AZ?