Many people like to leave their coffee machine on all the time so that the machine is hot and ready to use right at that moment that you want a coffee. This is especially the case with e61 style machine where the 4.5kg of brass brew group can take up to 30 minutes to get hot.
The solution to waiting for the machine to heat up is to leave the coffee machine on all the time. But should you do this?
Its really a question of balancing convenience with reliability and servicing cost.
Lets explain a little further....
Heat is a major contributor to wear on the internal components of coffee machines... the longer the machine on, the more times the pressure switch or thermostat switch on and off.... the wiring is exposed to heat for longer.... and the heating element is used for longer.
A machine that is on 24 hours a day would likely "wear out" 3x faster than a machine that is switched on for 8 hours a day.
We ask a lot from our coffee machines... To put it in perspective the typical household oven might be used for 1-1.5 hours at a time... often it is not used every day... compared to a coffee machine which is used every day often for 8+ hours.
Leaving your coffee machine on continuously will accelerate degradation of the wiring, pressure switch, heating-element, etc.... so you will be looking at higher maintenance costs over the life of the machine.
If you value convenience and are prepared to accept higher maintenance costs, then feel free to leave your machine on all the time.
If you want to extend the life of your machine then just switch it on when you use it and leave it off the rest of the time...
Perhaps consider putting it on a timer, so that it is switched on and hot before you need to use it... Many people use a timer in the morning to make sure their macine is hot and ready to fuel them for the day.
I would recommend leaving it off when not in use...