Well, there are pros and cons,, but not really a right or wrong answer.
Yes, contradictory I know.
Pro's
1. Fast access from sleep state
But, lets ask ourselves and find out, how long does it really take to start up?
If your system is old, it could take some time, in this case, Only shutdown if you are not going to be using it for more than 8 hours. Why? It will last longer, Heat and Power are an enemy to hardware. The longer and more used, the shorter the life expectancy.
But with SSD Drives, is 30sec or less a long time to wait to start using your system?
Sure, you can leave it on 24/7 and it could last 10 years, but it could also last 1, there is not one single person who can give anyone a definite answer to that question. Not one on this planet.
2. If you want to access the system from elsewhere via remote access.
3. When downloading large amounts of data.
Cons
There are many. Some already stated and obvious.
2. If the system is on and connected to the net, it is more prone to attack by hackers.
3. uses power, not saying that for any other reason than it uses power you are paying for.
I shut mine off when I'm not using it.
But if I ever leave it on for a extended amount of time,after I have completed a task I'll shut it down.
There is no real answer,, it really is a matter of preference.