Fairlight: What exactly does activating "Insert" do?

In the mixer panel we have a section called "Effects In" with the In button to be turned on/off.

The user manual (17.4.6) says about this:

Insert
Enables the routing of effects from Blackmagic audio interface hardware to outboard effects boxes
and back again. This button can be toggled to enable/disable such routing.

Ok so far - this means it has only use when BMD audio hardware has been installed and is in use, right?

Despite this - I was doing a test setup for a surround mix, put a stereo music into track 1 and setup the pan. In the mixer panel effects strip of track 1 I inserted two FX plugins: Neutron and Gullfoss
Order is set to EQ FX DY

According to the manual toggling on the "In" button should make no difference - but it does. It seems without enabling Insert the FX plugins are not used at all.

So my assertion would be that the user manual is outdated on that part and to use effect plugins you need to active Insert anyway (Fairlight does it automatically when you add a plugin to the strip).

Am I correct here? Shouldn't Blackmagic update the user manual to better reflect this?

The Fairlight Mixer Insert button toggles the Insert and bypasses inserted effects (plugins) and toggles the Insert Return (duplicated in Path Settings) in Fixed Bussing mode.

The Fairlight Mixer Insert button toggles the Insert and bypasses inserted effects (plugins) and toggles the Insert Return (duplicated in Path Settings) in Fixed Bussing mode.

Thanks for clarification, Reynaud. So it is the user manual in need of an update here.

Just a small update:
After reading through the newer DVR 18.5 user manual it seems the info has been updated:

Effects In:
A button to globally mute or enable all insert effects on a track (Fairlight FX, AU
or VST). Track FX and the built-in channel dynamics and EQ are not affected by this control

Do you know if it's actually bypassing the plug-ins by turning them off completely so they don't affect performance, or is it just bypassing in the sense of muting?

The Insert button only bypasses.

Individual plugin instances may be disabled via the insert slot's "more options" drop-down (hover over the instance to reveal the bypass, controls, and more options buttons).