Water filtration maintenance affects cafe espresso more than machine tuning

My confusion with water filtration maintenance for espresso quality is that the idea makes sense on paper, but practical execution looks much less clean. The more I ask around, the more I hear opposite conclusions from people who are all experienced. That usually means the answer depends on context more than people admit.

For members here who have worked with water filtration maintenance for espresso quality, what condition makes it useful and what condition makes it mostly noise?