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 either audio device or JACK ports. While jack ports are visible to other JACK applications, ALSA ports are only useful for patching in audio equipment external to the computer. If inserting a software processor is required, a plugin would be the first choice. If a plugin is not available then the jackd audio backend would have to be used. This is not very common any more but there are some older jack clients that require using jack.
Inserts work the same as the inserts on analog consoles except they are not normalled like most 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 period of latency, which can be measured and compensated for during mixing, but not during tracking!