Consider a standard laptop build. Now suppose you leave it running (not just plugged in) permanently. To what extent will this produce hardware degradation or increase the risk of hardware failure?
If it's not in a clean room (by which I don't mean your mom thinks it's clean, unless your mom works at a nano-fab or assembling/recovering hard drives), it will pull in more dust, dirt, hair, lint etc. running than it will sitting powered down. Dust, et al, gradually reduces the effectiveness of the cooling system, so depending on its thermal control logic it will either run hotter or slower as a result. Running hotter does impact life expectancy of most components. How much (your actual question) would basically be time running (total) divided by time running (actual use) – any more than that is too variable based on the conditions of the room (have you got pets and various other environmental factors) , and the design of the laptop.