Here's a hypothetical but a realistic scenario that not having reproducible builds is a major issue:
1. I create an app for a client.
2. Client installs the app on their 10,000 enterprise mobile devices and trains the users.
3. Month passes. I've changed everything in the app.
4. Major security or outage event happens. I need to change a line in the app and those 10,000 devices need to be updated ASAP.
5. If I can't checkout the old version, change the line and ship it without wondering "what else will change in this build" - then both me and my client are going to have a bad time.
It will take two weeks for a full qa/audit of the app and there's no time for that.
1. I create an app for a client.
2. Client installs the app on their 10,000 enterprise mobile devices and trains the users.
3. Month passes. I've changed everything in the app.
4. Major security or outage event happens. I need to change a line in the app and those 10,000 devices need to be updated ASAP.
5. If I can't checkout the old version, change the line and ship it without wondering "what else will change in this build" - then both me and my client are going to have a bad time.
It will take two weeks for a full qa/audit of the app and there's no time for that.