Even before using SP, I assume you used these mask types on your older skins?
Even in the few years prior to SP I have increasingly used masks and adjustment layers where appropriate. Before that I would just alter the layer directly but the nice thing about using a mask or adjustment layer is that it is non-destructive. Some examples:-
I like to age wing walkway lines and maintenance signs by partially erasing them. The simplest way to do this is to use a full size erase tool set low density and medium opacity and apply it a few times to the whole layer. Then use a smaller erase tool to wear a few areas more heavily. Now though what I do is create a "show all" mask for that layer. Then I apply a full size, low density, medium opacity airbrush tool to the mask, basically spraying lots of grey or black dots all over the white surface of it and then a smaller airbrush tool for specific areas. Both methods give the same effect, a load of dots where the lines and signs are partially or fully erased. The difference is that if I want to reduce or remove the ageing effect later I can either alter the mask's opacity slider to do so or use a white airbrush tool to reverse the specific ageing. With the old erase method I'd have make sure I kept an un-edited copy of the layer to erase again, if not I'd have to recreate the whole layer from scratch.
It is not uncommon to have areas of a plane that have been repainted in the same colour but that don't blend in because the new paint is a lot less faded and weathered. Previously what I'd to mimic this effect is to create a layer with patches of a less faded shade of the base colour. Now what I do is create a hue/saturation/lightness adjustment layer above the base paint layer. This is set to increase the saturation and usually darken the layers below it. I then apply a negative image command to the adjustment layer turn the effect off before spraying those areas that I want to be less faded white. In these specific places this reverses another overall paint fade adjustment layer I use to desaturate and lighten all the paint. Once I have the adjustment layer done I can then alter the effect with sliders until I get the level I want. Not only that but I can copy and paste the adjustment layer's data into a new mask layer that I then place at the top of the weathering group. This mask layer erases all the weathering but on the freshly painted areas only. Again I can use an opacity slider to reduce this effect to a level I like.
When creating paint chips I like to have chips near the fasteners and on edges of access panels, but not on the panels' and fasteners' black lines themselves as this ruins the effect. My old method for doing this was to duplicate all the panel line and fastener layers, set these duplicates to 100% opacity and then merge them all into one layer. Then after creating the paint chips I'd move to this merged layer, select the whole layer's data, go back to the paint chip layer and hit the delete key. This deleted all the paint chips on the panel lines and fasteners but left the rest. Now though what I do is turn the merged panel line layer into a mask. The method is to create a solid white layer below the merged panel lines and then merge these two layers. This gives a white background to the black panel lines. I then copy and paste this data into a mask layer that I create for my panel line layer. The advantage of doing it this way is that when I edit the paint chips on my next skin the panel line erasing happens automatically, I don't have to select the merged layer and hit delete. Its a small time saver but every little helps.