You never vary aperture when taking bracketed exposures to merge to HDR. The depth of field would vary from exposure to exposure, making things inconsistent when you merge them. It's shutter speed you vary.
My point is that with 2005-era DSLRs, I had to use HDR techniques (or strobes) to, say, correctly expose a room and the environment out a window. Shooting into the sun, I'd have to use HDR, polarizers, and/or ND grads to expose both the sky and the foreground. With my D750? I've got 4 stops more dynamic range and the situations where I need HDR have almost all gone away. I can get the same thing from a single RAW exposure.
These days, HDR only seems necessary if you want to have ridiculous tone mapping where you pull in your global highlights to be within a stop or two of your global shadows and still keep the noise levels down.
My point is that with 2005-era DSLRs, I had to use HDR techniques (or strobes) to, say, correctly expose a room and the environment out a window. Shooting into the sun, I'd have to use HDR, polarizers, and/or ND grads to expose both the sky and the foreground. With my D750? I've got 4 stops more dynamic range and the situations where I need HDR have almost all gone away. I can get the same thing from a single RAW exposure.
These days, HDR only seems necessary if you want to have ridiculous tone mapping where you pull in your global highlights to be within a stop or two of your global shadows and still keep the noise levels down.