I have been using Gmail for over 5 years. The service has helped to significantly simplify tasks, and the entire workflow. We are pleased with the fast search by correspondence, which is very convenient when searching for old letters. The service is also integrated with hangouts. That is, on the road, it is easier for me to write from the phone through hangouts, and at work from mail, without being distracted by unnecessary instant messengers.
Gmail allows me to use my own theme, set up reminders from the calendar with notifications in the form of letters and SMS ... Moreover, by installing gmail on a mobile device, you can store your contact database on the server for quick recovery.
Plus, mail works closely with Google Drive. I save a photo there, 15 GB is enough. Files for collaboration are also placed there.