Personally, I’ve never used snapshots. (I think they are an extra-cost item, and I’m not certain of their usefulness when there’s a live database running.)
The way I think about backup frequency, is how would I feel at the time I need to restore the backup? If I’d lost a month’s worth of member conversations and contributions? That would feel pretty bad. I had a responsibility to the community, and I allowed their work to be lost.
Against that, if I’m running in a limited disk-space situation, I want to balance the disk use. What I’ve done in practice, and I should probably review this, is to backup every two days and retain four backups. One of my moderator team automatically pulls a copy of the backup directory every night, so we have an offsite copy. We stand to lose half a week of contributions, in the case of disaster.