I've found Spectacle leaves a bit of padding space under where the dock folds out - potentially useful, but unwanted in my case, and I wasn't able to find a setting to change that behaviour.
I use BetterSnapTool instead, which seems to have a better collection of settings and solves my (admittedly minor) gripe with Spectacle.
I use BetterSnapTool instead, which seems to have a better collection of settings and solves my (admittedly minor) gripe with Spectacle.