Email client or web interface? I've seen a lot of people

Client applications are good at staying responsive while moving large batches of messages around between folders, either manually or via filters. You can also avail yourself to loads of plug-ins/extensions for calendar integration, attachment management, etc.

If none of those things apply and/or your web interface of choice already includes the integrations you use--as many do nowadays--then the browser might suffice for you. It mostly does for me, though I am occasionally bothered by how slow it can be to load stuff and respond to actions.

I use thunderbird because I don't need a Web client. Works well when you have a desktop computer and a phone.

All mail servers are simple database. Data are transmitted by network protocols. When I'm using webmail, automatically webpage try to get other foolery as ads on webpage. I must configure a Firefox profile to use Outlook webmail.
Then Mail client is lightweight to use.