As long as there is a stop-down lever present, but no aperture follower, the only way the camera can make a correct exposure is on-the-fly metering when the camera actually stops down the lens for taking a picture. If non-CPU lens data is entered, however, the camera at least can make a quite reliable estimate of the exposure in advance, before actual shooting takes place.
If there is no aperture lever in the lens itself, metering would be simply at the set aperture. Possible the metering options then would be restricted to A, M in this case. Of course, if the mounted lens has no aperture linkage and has a preset aperture ring, like old lenses from '50s or '60s, then there is a high risk of getting the exposure entirely wrong (unless the in-the-fly correction is performed, which only can be done with ISO or shutter speed adjustment).
For myself, I have verified that CPU-modified lenses* work as they should, with the caveat aperture has to be set from the camera side. Thus, good bye to the ergonomically optimal approach of using both hands. That's the price to be paid for "progress".
* of which I have a large number in F mount