QNH ops on an aircraft equipped with the QFE option is what I had in mind. To make sure you did not set QFE by mistake, which is ergonomically rather simple slip of a finger.
Some people need just to set the value, others both the number and its reference. The latter crowd might find it very useful to announce the QNH/ QFE (in blue on PFD) during the checklist response.
The design: ...... _ _ _ _ _ _ SET allows for both.