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Since it's inside vim, it's very lightweight and fast. It fires up quickly and it does all operations painlessly.
Pro Mouse-free interface
It's practically vim, this means that the whole interface is mouse-free, this increases development speed significantly since you are only using the keyboard.
Pro Helpful to people who work a lot inside the terminal
Using command-line tools (vim/git) keep you stick in the terminal.
Con Not for people who are not used to vim
Since this is basically a vim feature, it's clear that people who aren't used to vim and it's keyboard-based interface would find it very hard to work with vimdiff.