I race every two weeks, luckily in UK we have 5k parkruns so we don't need to pay a fee to race. This usually give me incentive to train, before this schedule i never entered a race unless i knew i was in good shape, this meant it took me several weeks before i would enter a race.
If you like to reach your potential, then the racing often wouldn't be such a good idea. For me personal I'm definitely not going be a elite runner, so i would regret not racing as often as i could, after all this is a hobby. I also don't understand why people here are reluctant to pay for a race fee , especially if racing is your hobby , most other people who are have sporting hobbies usually spend some money on their hobbies because they enjoy it and usually one of the few things that give their lives joy. So i see no problem with spending money on races, obviously there is a limit to this depending on budget and other factors.