While separate translucency is enabled DOFRecombine will incur a cost even when not using DOF (Scale of 0 or blur size of 0). Maybe we can check to see if those values are == 0 (meaning DOF is effectively disabled) and not incur the cost.
There will also be a BokehDOFRecombine cost even when using other DOF methods such as Gaussian. Although in my tests the cost was very trivial (0.04 ms) the licensee is getting a cost of .34 ms.
There will be a cost for BokehDOFRecombine.
There is no cost while the DOF Scale is 0 or the Blur Size is 0.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-45129 in the post.