What do you mean disadvantage...? Every single Linux Distribution has its advantages and disadvantages over another. If you want to know disadvantages to Ubuntu, be specific in terms of what and compared to what other distributions?
The real disadvantage is that Ubuntu tries to stay near the 'bleeding edge' of Linux development, so it's less stable than many other distros, and a lot tends to change in the six-monthly updates to the point where after a year or two a fresh install may be faster.
On the plus side, that means you get new features faster than many other distros.
There's alot of commands for every operating system. At least most of the Bash commands are named in some sane way, and they come with extensive documentation. Some of the Windows commands still have me wondering what the designers were drinking when they came up with them, and they have no documentation unless you google them.
This isn't really a disadvantage of Ubuntu anyway. It's a disadvantage of Bash (or Linux I suppose) if you really want to call it a disadvantage. Nobody needs to learn them all anyway. Learn what you actually need to use, and if you forget how to use one you just bring up the manual page for it.
There is a GUI alternative for most answers given down here, same for the info frequently requested. It's just far faster to ask somebody to type "blah blah" into a command line than to describe how to navigate a set of menus and click on button x, y & z.
Seriously you can install, run and maintain Linux without ever touching a command line nowadays.
Yep. There's very little need to use the command line if you don't want to, both in Linux and Windows. You're missing a lot if you don't get to know the command line in both instances, but that's just my opinion.
I don't use the CLI in Windows much (it's horrible anyway, I can't even copy/paste properly nor is there a persistent history), but I use it in Linux alot even though there are perfectly adequate GUI replacements.
Does CLI mean command line interface?...if so ,I love CLI in windows. I agree it isn't as good as Linux's, its more then enough to perform simple and common tasks easily and quickly without the need for messing with GUI.
Oh for sure, it's still good for getting verbose output from programs and having fine-grained control over certain tasks (the GUI front-end to the defrag utility is useless). But it doesn't come close to Bash. Plus it doesn't have man pages