For instance, decals are easier to apply, and will last longer, on a gloss surface.
Here's a quick breakdown of which surface is better for various techniques:
|Overall washes||Oil filters|
|Decals||Panel line washes|
|Oil filter (dot method)|
Knowing which sealer to apply for which technique will help you decide in which order to apply weathering techniques.
For instance you should always apply a gloss layer before and after applying decals. However putting gloss over pigments/pastels will likely make most of your effort disappear.