I use a lot of washes myself, very useful tool, they get less effective the larger the scale but still very useful. Where they shine on larger scale stuff is stuff like leather to show wear etc.I used to use an ink wash on faces for larger scale wargames figures before adding the final highlights. The big advantage is that a suitable water basedwash will dry relatively slowly, allowing the shading pigment to settle into the creases etc giving a subtle shading effect without you having to try and blend it all in.
This will give you the idea:
I use washes for painting pretty much everything these days - figures, vehicles, scenery.