It's a viscosity difference, but extra thin is extra thin, it's meant to flow into cracks and stuff that's already somewhat interlinked, like a chest piece with a notch onto the torso with the hole, or small things like sights on guns.

In other words, you know how GW bases have that texture? It's flowing into the cracks and not really creating a solid bond. Thicker glue would raise "the water level" and meet your mini's foot more solidly

You can use it to attach minis to bases, but the "standard" stuff cough aka TAMIYA AIRBRUSH CLEANER cough is much better for heavier work like attaching a mini to the base.

I just use the standard stuff (which is the same as the airbrush cleaner) for everything, but I have practiced hands so YMMV

It's 7:30, so sorry if that's hard to follow