Preferences are:

• A fork in your app. You will forever have a divided user base.
• A time sink. The eat up support time, programming time, and debugging time.
• A cop-out. When you can’t decide, -add a preference. It’s how bad software gets worse.
• Confusing. They often have far reaching effects on usability that the user has no way of visualizing.
• Ugly. Those fiddly screens full of toggles and buttons are a mess. A mess to use, and a mess to design.
• A chance to fail. If you allow your users to customize your app so that it is accidentally less useful to them, -you’ve missed the point.
• Sometimes Necessary. Awful, but necessary. Things like “time zone” or “currency indicator” are unavoidable preferences.

Make sure the list is small, and deal with them gracefully as possible.