Dbuffer decals vs directly lighting (performance cost)

I know switching on Dbuffer Decals comes at a “slight” performance cost (on the CPU).
The way to not need Dbuffer Decals switched to on for decals to work is to use decals in direct light → put a stationary or movable light on the decals.

My question is simple: which one is preffered, performance wise.
a) switching on Dbuffer Decals so there is no need for stationary or movable light
b) use a stationary or movable light to directly light the surface that will receive the decal


I am interested in this as well!