No i don't think by turning on 24/7 will make a healthy PC.
Reason being the lifespan of electronic components on the board or other stuffs like HDD and other moving parts goes by the hours of usage.
By turning off your PC and turning on when needed not only save your electricity bill. It helps in prolonging your products lifespan.
A ceramic capacitors lifespan by theory could last the most 6 months if everyday is being used.
Ceramic, polyester, monolithic, tantalum and electrolytic are a few examples of material used in the capacitors/resistors/fuses and other components.
IC chips have a expectancy of at most 10years.
Of cause i have yet to see any boards using tantalum capacitors.
With that the lifespan of that could last 20 years.
Anyway i'm not here to tell you what is good or bad. A PC components are actually based on the number of hours you used. Whether it breaks down faster or not is also depend on how all the electronics component last. Or the integrity of the components that are build from factory.