Debris in the faucets (and occasionally the toilet valve).
Other than trash (saw dust typically) in the lines at construction time, the number one cause of clogged fittings is the hot water heater.
As the anode deteriorates due to galvanic action, bits of anode and calcium scale collect in the bottom of the hot water heater. These bits can be swept into the hot water pipes and really clog up the works.
The cold water faucets and the toilet are not immune since there is a low pressure formed at the cold water inlet of the hot water tank when you open the cold water faucet or flush the John. This can suck bits out of the hot water tank and into the cold water lines.
Regular maintenance of the hot water tank, including anode replacement when needed, and a thorough flushing of the tank with a flush rod (like this one made by a member) will minimize the chance of a problem.
Lou and Laura with Bella - German Short Hair Pointer
2008 GMC Sierra 2500HD Crewcab SB Allison Duramax
2010 Flagstaff 8526RLWS - Superglide 3300
HAM CALLSIGN - KC3FFW