I also used it for a couple of projects and I found it extremely useful when I was a beginner at PHP and web development in general.
Yii shows the patterns used every day in web development now and therefore it is extremely useful for people who want to start web development with PHP. Also it has some disadvantages (or it had at least, I am not aware of the framework's state now) - e.g. testing (tdd?) is not so straightforward like it is in other, let's say "newer" technologies.
And my advice lastly: I do not know how good you are in PHP or web development but if you plan to use PHP in further developments then Yii is a good choice - I have not used it in the last 2 years but it was good 2 years ago as well. Maybe there are some other good frameworks now but give it a try at least on a smaller project.