I do not completely turn off my MacBook Pro and I only sleep it.
Are there any limitations to consider when doing this for several months in a row?
There's actually some validity to “Have you tried turning it off and on again?”.
Extremely simply put: Over the course of being on, the OS accumulates a lot of “leftovers” from all of the processes that've been running (Automatic garbage collection isn't perfect). When the system is restarted cache is purged and only needed processes are started. Sometimes processes that run for a very long time can use more memory and even — at times — stop working. Also, it's not all apps that clean up properly after themselves which can lead to unused processes taking up memory and/or CPU cycles.
OS X handles this excellently (compared to Windows) but I think it's impossible to create an OS that is entirely immune to the "littering" of a system that is often used over extensive periods of time.
Note: This is just my experience from 10+ years working with computers. I probably can't give a scientifically correct explanation :)
I almost never turn off my (Mid 2013) MacBook Pro and can't remember any issues. In fact the only time I restart it is when an installation requires it.
It's probably not a bad idea to have a password on wake but that would be a personal choice rather than a hard and fast rule.
I think what you loose is security, or you at least make your pc more vulnerable while it does not necessary needs to be. If you turn off your mac, it is turned off, and no services are(or shouldn't be - correct me if I am wrong)running in background as konqui said in the post up. Turning off your wifi, or taking off internet cable should solve this problem.
Other think you loose is a bit of performance, because you have lots of other things you maybe started before and not necessary need now. After restart, your ram is free from leftovers from other apps, and swapping. And you can read here lots of complaints from people that their ram is not freeing the memory as it should be, and their macs are a bit slower.
What you gain is a bit time, which you loose for booting up your mac, and starting apps to your desirable state. Which I expect it was in before you would restart or turn it off.
Personally, I don't think there is any problem in putting it to sleep only. Critical updates from apple will make you restart your mac from time to time. And if there was a problem, there would be significant complaints from apple community.