Not exactly sure if you are suggesting small shoaling fish in with the Betta, but male Bettas are not community fish, so they are always best alone. I know some say they have had success with a Betta in with other fish, but this is not normal, it is the exception, and if we care for our fish which I trust you do we will not force them into a scenario that is more likely to fail than maybe work. A normal healthy Betta males will not appreciate other fish in his space. And there are other threads here where the peace lasted for a time until overnight the Betta decided it had had enough of the other nuisance fish.
This also works in reverse. Many of the small peaceful shoaling fish like tetras, etc, will turn to fin nipping when they are faced with a Betta day after day. So this can be not only bad for the other fish, but bad for the Betta.