It depends on the swatches; if they are the type of swatches that seem to be done to fit an aesthetic (or to just look “good”) then I put little trust in them in terms of telling me anything meaningful about pigmentation, finish, application, blendability, and even texture. Whether they’re done with fingertips or brushes, over primer or on bare skin, so long as they look “real” and are trying to show the product as-is vs. make it look “good,” then it often tells me about pigmentation, adhesion to the skin, blendability, and powderiness (if present).
I don’t think that swatches always tell the full story, but I’ve swatched enough to know that I can tell a lot by swatching that usually confirmed by applying it to the intended area. There are some types of formulas that work better “in practice” than just swatched, and then these days, some of the more silicone-heavy formulas look better swatched than they perform in practice. I use them as a baseline–they can be a guide, but I wouldn’t assume that what I see swatched is what I’d get in practice. I think they’re particularly good for getting an idea of color and finish, how they might sit on skin, and things like that.