Mobile app for a website vs browser view [on hold]

I have noticed that many websites have their own mobile apps.

For developers, What is the benefit of creating mobile app for a website? In which cases it is better than viewing it using browser?

From users point of view it is not always good. Why should I install separate app for every website I often visit? Mobile app seems not always to be faster than browser, and they can take a hundred of MBs in some cases. UI of mobile apps is not always better than that of their websites, and functionality is usually less.

Which points can be crucial when determining if there is a need of mobile app for a website?