I do use 2 desktop email clients; claws-mail and electron-mail, an unofficial ProtonMail client https://github.com/vladimiry/ElectronMail. I hate the in-browser web clients, they're so freaking slow and cluttered, thought proton mail's is quite usable. People use desktop email clients because they make it easier to manage their email accounts. Imagine having 10 mail accounts(I don't, but I know people who do)for different purposes, and having to launch a browser, visit the mail sites, log in, wait for the whole thing to load ... with a desktop email client they just have them at the reach of a click.I don't use any email client and never have and I never have understood why anyone needs to use an email client.
If I want to sent an mail I log into my email and compose a message and send it.
I get an alert when people send me an email.
I'd use thunderbird, if Mozilla ever bothered to provide a systray functionality. I tried Mailspring, and I kind of liked it; tons of useful features. Unfortunately, it can be quite a resource hog. https://getmailspring.com/Thunderbird is open 24/7