I make snapshots every hour for 24 hours, every day for 7 days, every week for 4 weeks and every month for three months. This keeps the number of snapshots reasonable while keeping most stuff around should you accidentally delete or overwrite it. I can see a good argument for more fine grained snapshots (e.g. every few minutes) but I think I'd limit that to directories (and thus FSes) known to have frequent updates.
I sometimes blow away all snapshots if I have a big clear out or rewrite of data, or else that stuff sticks around for months.
I sometimes blow away all snapshots if I have a big clear out or rewrite of data, or else that stuff sticks around for months.