Inserts are signal tap points that can be placed anywhere inside a channel strip. Unlike Auxes, they will interrupt the signal flow, feeding the signal from before the insert point to its Insert send(s), and connecting the remainder of the channel strip to the Insert return(s), both of which are JACK ports which are visible to other JACK applications.
Inserts are the JACK equivalents of normalized switching jacks on an analog console.

An insert allows to either use a special external DSP JACK application that is not available as a plugin, or to splice an external analog piece of gear into a channel strip, such as a vintage compressor, tube equalizer, etc. In the latter case, the inserts would first be connected to a pair of hardware ports, which are in turn connected to the outboard gear.

Disabling (bypassing) an insert is done by clicking on its LED in the processor box.

When an insert is created, the signal will be interrupted until the relevant connections to the insert ports are made!

Inserts will incur an additional JACK period of latency, which can be measured and compensated for during mixing, but not during tracking!