Analysis of information sources in references of the Wikipedia article "Dacă și numai dacă" in Romanian language version.
It is common in mathematical writing
While it can be a real time-saver, we don't recommend it in formal writing.
Theorems which have the form "P if and only Q" are much prized in mathematics. They give what are called "necessary and sufficient" conditions, and give completely equivalent and hopefully interesting new ways to say exactly the same thing.
