Nodri wrote:
Pigments are applied after the clear coat if a clear coat is applied at all. Wargame minis, due to handling, are generally clearcoated to protect the paint. Display models are often not clearcoated because varnish changes the underlying color.

If you clearcoat over the pigment, you will be adding solvent & binder to pigment. Pigment+binder+solvent=paint. At this point, you will destroy the dusty effect of the pigment and you may as well airbrush a dust-colored paint instead (which is a perfectly viable technique by the way). Pigment fixers are solvents & binders that are specifically formulated to have a minimal impact on the appearance of the pigment. Again, though, minimal doesn't mean zero.

 Nodri wrote:
At this point, you will destroy the dusty effect of the pigment and you may as well airbrush a dust-colored paint instead (which is a perfectly viable technique by the way).

 Peregrine wrote:

I don't think this is entirely true. You'll modify the appearance of the pigments, but you won't change their behavior. You'll still get things like settling in the small recesses of tank tracks, which would be impossible to duplicate with an airbrush (or conventional brush). So it can still be worth using them even if you know the varnish layer is going to be necessary.