Vim is a powerful, portable, keyboard based text editor. Being text-based, vim is lightning fast, with an incredible set of features developed over its multi decade existence.
Pro Lightweight and fast
When compared to modern graphical editors like Atom and Brackets (which have underlying HTML5 engines, browsers, Node, etc.), Vim uses a sliver of the system's memory and it loads instantly, all the while delivering the same features. Vim is also faster than Emacs.
Pro Extremely portable
Vi/vim exists on almost all Unix-like platforms. It's the de-facto Unix editor and is easily installed on Windows. All you need to make it work is a text-based connection, so it works well for remote machines with slow connections, or when you're too lazy to set up a VNC/Remote Desktop connection.
Pro Keyboard-based, mouse-free interface, and trackpad support
There's no need to reach for the mouse or the Ctrl/Alt buttons again. Everything is a mere key press or two away with almost 200 functions specifically for text editing. Vim does support the mouse, but it's designed so you don't have to use it for greater efficiency.
Versions of vim, like gVim or MacVim, still allow you to use the mouse and familiar platform shortcuts. That can help ease the learning curve and you'll probably find you won't want to (or need to) use the mouse after a while.
Con Poor feature discoverability
Though basic features like syntax checking, autocompletion, and file management are all available out of the box or with minimal configuration, this is not obvious to new users, who might get intimidated or assume they need to install complex plugins just so they can have this functionality. Other features new users might expect to find embedded in Vim, such as debugging, instead follow a UNIX-style model where they are called as external programs, the output of which might then be parsed by Vim so it can display results. Users not familiar with this paradigm will likely fault Vim for lacking those features as well.
Con Difficult learning curve
You'll spend a lot of time learning all the commands and modes supported in Vim. You'll then spend more time tuning settings to your needs. Although once it's tuned to your needs, you can take your
.vimrc to any machine you need and have the same experience across all your computers.
Con Requires Brain Mode Switching
When editing in vim, you have you use the vim keys; when editing in every other window on your PC, or in Word or Excel or other application, you need to use the standard system key combinations. Learning the vim combinations can actually make you SLOWER at everything else.
Con Consume brain energy for editing that should be used for logic
Text editing in vim is awesome, but it requires thinking about combination of commands. In other editors, you don't have to think about how to delete this part of code. You just think about how to implement a feature, what is a good design for this code. Even after you get used to using vim, it still requires your brain for editing.
Con Doesn't play nice with the system cut/paste mechanisms
This can be worked around somewhat if you disable mouse for insert mode. You can then right-click your terminal and use paste like you would anywhere else in a terminal.
But it still doesn't feel right when the rest of your system uses Ctrl-C/Ctrl-V, and you have a system clipboard manager, and so forth.