Running your components and cables for some arbitrary length of time when they are first purchased isn’t helpful, but letting them power on and sit for a few minutes before watching movies or performing calibration is.
With even simple home theater systems now needing universal remotes [Hack #84] and calibration to perform well, a lot of well-meaning folks have passed around some home theater myths, or at best, misunderstandings. One of these is that you need to burn-in your equipment. Burn-in is a term used to refer to running your gear for some arbitrary length of time, usually several hours, to help it perform properly. You’ll most commonly hear about burn-in when talking about speakers, which often can benefit from this sort of treatment.