Not a 737, but in our outfit we use the Rad Alt call as a final backstop against IMC descent below the minimum (whatever that may be).
For a Cat 1 ILS, we set it at 150ft.
For an NPA, we set it at 300ft.
When the Rad Alt calls "Minimums" an immediate go-around is mandatory unless the PF has obtained Visual Reference.
On a visual approach, we set it to zero to stop it calling.