Preface: I'm aware of the many strategies out there for determining vertical font metrics, including how to account for some default leading, so know that my question isn't about the *how*. It's more about the *why*.
Question: When it comes to vertical metrics, is it useful (necessary?) to program-in a reasonable amount of leading, or do you find that leaving the values as close to "solid" as you can works better because apps will choose their own line spacing anyway? I know that many apps have no capability to adjust line spacing, so some internal leading would be useful. Maybe that answers my own question, but what is your experience on the matter? What other pros/cons should a designer like me be aware of when planning internal leading?