Ups,
Jaques ask for varnishing AFTER the painting.
So as Kostis has mentioned. The glossy varnish on armored miniatures is to stop the silvering of the film surrounding the decal and it stick better to the surface. The most obvious are the national signs on the wings and fuselage for planes. After that dry varnish.
So there is no real reason to do first glossy varnish and after that dry varnish to a figure.
No decals, no glossy varnish is need.
Sometimes it happen that some of my figures get decals.
Small decals !
A brassard, a sign to the steel helmet.
I cut it as small as possible. No glossy varnish. Decal softener. Especial for the brassard.
Decals for shields (Vikings, Knights) I haven´t done that so don`t know, sorry.
Side note:
In the beginning years of serious modelling I do glossy varnish at last to the painted eyes.
But not for long. I did`t saw any improvement to the figure.