Most modern electronics will last longer if left on all the time rather than turned on and off regularly. Thermal cycling is the culprit, as is the initial power surge when turned on. Probably the best example of this is a common tungsten light bulb. I had a ceiling fixture in my dining room controlled by a dimmer, and rather than turning the dimmer completely off, I always left it at the lowest power setting, at which point the bulbs' elements barely glowed, but did not go completely off. The bulbs in the lamp never burned out, even after 8 or 10 years. They were still going strong when I sold the house.
More to the point, I almost always leave my computer in sleep mode, not only to reduce thermal stress, but it also ensures my Windows OS automatically updates to the latest version of whatever item needs updating, especially security updates. I never turn off my home networking gear -- router, switches, network drive, phone adapters, etc. Anything using an external power brick will be fairly well isolated from the mains.