smoking tube

Are there pros and cons of leaving the water in a water pipe or other smoking marijuana accessoriess?

I do not smoke, but a friend was curious and wanted find if there are any pros and / or disadvantages of leaving the water in a water pipe

I know nothing professional. I watched a couple of idiots drinking, thinking I would do something, but just got sick. One can think of is that if you leave the water there, does not leak. It is one of the worst smells and is hard to get rid of him.