The [Advanced] or custom retention policy allows you to configure a more flexible retention policy. It allows you to keep a set of snapshots of all backup files based on the time of the backup Jobs.
For example, you can configure the advanced retention policy to keep the following sets of backup files to mimic the retention policy of the old days when you were still doing tape rotations:
- All files available within the last 7 days
- All files available on the last 4 Saturdays within the last 28 days
- All files available on the 1st day of each month within the last 3 months
- All files available on the 1st day of each quarter within the last 12 months
- All files available on the 1st day of each year within the last 3 years
To accomplish this, you need to setup your advanced retention policy as follows: 
- Type = Daily; Number of snapshots to keep = 7
- Type = Weekly; Frequency = Saturday;
Number of snapshots to keep = 4 - Type = Monthly; Frequency = Day 1;
Number of snapshots to keep = 3 - Type = Quarterly; Frequency = Day 1 of Jan, Apr, Jul, Oct;
Number of snapshots to keep = 4 - Type = Yearly; Frequency = Date 01-01;
Number of snapshots to keep = 3
If [Remove retention files for overlapping policy] is enabled, only one snapshot for the overlapping policies will be kept. For instance, the latter 3 policies above overlap on Jan 1st, therefore only one snapshot will be kept for Jan 1st.