If you leave your computer on for a long period of time and you are not working on it, the display will finally turn off after a preset period of time, but your computer’s hard drive will continue to work, this happens for example when you want to download something from the Internet and you leave the computer to do it without working on it. The display of your laptop will turn off (to save some energy), but the Internet connection will be available and your hard drive will continue to work because your computer is downloading something. There isn’t any problem if you keep your MacBook Pro on all the time, but it is important what your computer is doing in the mean time, because if it is overheating over and over again this could mean trouble.
The things you should know are that your MacBook Pro is using a lot of electricity if you always leave it on and you should keep all the vents clear and don’t run all day CPU intensive task, because they could overheat your laptop. An option could be to put your laptop to sleep, this doesn’t mean shut down, because when a computer in on the sleep mode all the applications, the hard drive, the CPU are in stand by mode, which means that they are not turned off and they are waiting for your command.
If you don’t use your laptop over night, you should keep it in sleep mode because the computer will use less electricity and if you need to do something very fast on your computer, all you have to do is to press a button and the computer will be awakened and will wait for your command.
Also if your computer has the hibernate option, you can put it in to hibernate mode, because it is better than just to keep it on. The hibernating mode is faster than a normal boot and you will have all the data saved the way you left it. If you want your laptop’s battery to work well, you should let it run out completely once a month and this means that you have to unplug your computer. And when you want to charge it, you should turn it off, because if you charge it while you are using it will take a longer time to charge and your computer will keep emitting heat. Overall, it is all right to leave your MacBook Pro or any Mac on all the time, but at least once a month you should let the battery run out completely and turn it off for just one night.