A snapshot records your whole risk picture as it was on one date: counts by band, by risk type and by governing body, and how many units were outside appetite.
When they're taken
At each quarter end, automatically, on your tenancy's own quarters.
On demand, whenever you take one (for example before a board meeting), with a label.
Each snapshot says whether it was scheduled or on demand, who took it and when.
What they're for
The trend chart on the Overall Risk Picture.
"Since last quarter" movements on Home and the dashboards.
A fixed "as at" figure for reports, which doesn't change when scores change later.
Testing's Assurance Picture is snapshotted at the same moments.