Common usages include gating, compressing, equalizing and for reverb effects that are specific to that channel or group.
[1] Inserts can be used as an alternate way to route signals such as for multitrack recording output or line-level direct input.
Unbalanced inserts can also be a pair of jacks such as RCA or 1/4" TS (Tip Sleeve) phone connector.
Of the mixers using this kind of dual-purpose insert jack, most are designed with tip send, ring return.
[a] Inserts on analog mixers appear in various locations in the signal flow, depending on user configuration or the vision of the designer.
Similar to line-level inputs and outputs, insert points are found at a variety of signal levels.
Both analog and digital designs include sufficient headroom to allow transients exceeding the nominal level to be handled without distortion.