Part One: Strategy · Deciding what to build
Removing a feature upsets the few who use it. Never removing anything makes the whole product harder for everyone to find their way around.
Products only grow. Every feature has a few people who rely on it, and they write in when it is threatened. The many for whom it is clutter say nothing, because nobody complains about a menu item they have never clicked. So removal always looks like pure loss.
The cost of keeping things is real, and nobody sees it being paid. Every screen has more on it. Every newcomer has more to learn before they find the part that matters. Every change has to be checked against things almost no one uses. And some features should never have been built.
The few are still real people. Someone who built their work around a feature was given a kind of promise, and taking it away carelessly breaks that promise. Removal done properly has four parts: find out who depends on it, tell them early and plainly why, give them another way to do the same work, and let them take their material elsewhere if they would rather.
Firefox once had Live Bookmarks, folders that filled themselves with a site's latest headlines. Very few people used them, and they cost real work to keep safe. Mozilla announced the removal in October 2018 and made it that December, in version 64. Each one became an ordinary bookmark to the same site. The feeds were saved to a file on the person's desktop that any feed reader could open, and a help page listed replacements.
In a large company nobody owns the old thing, so somebody has to be given it. Whoever makes the decision, the case for it is two things anyone can bring: the count of accounts that use the feature, and the plan for them.
Therefore:
Regularly look for what almost nobody uses and remove it. First find out who depends on it, tell them early and plainly, and give them another way to do the same work.
In practice. Pick one setting. Find out how many accounts have ever changed it from the default. If it is a handful, write to them and ask what they use it for.
Goes with. This is SAY NO BY DEFAULT (23) applied to the past. Do it with the care of CHANGE SLOWLY WHAT PEOPLE KNOW (56). What cannot go yet can move out of the way: SHOW A LITTLE, OFFER MORE (68).
Source: Mozilla Support, "What happened to my Live Bookmarks?" (2018).