While there is no definitive answer as this is totally up to the user, let me stress this.

MAKE REGULAR BACKUPS!

Now with that said, personally I would make a backup of my Powergold data at least once a day, at the end of your workday. This is above and beyond the Automatic backup that Powergold creates daily the first time you close the program on any given day.

Where to store your backups.

By default your Automatic backups are saved in your data folder. i.e., C:\Program Files\Powergold\MyData for a database stored on your local machine.
For your regular backups I would suggest using an external drive and/or a network folder. This way you have a backup that is stored away from the local machine in case of Hard Drive failure.