An email client is a specialized program designed specifically for checking and composing email. You can connect, download all your email, disconnect, and read the emails when you want. This is a very nice ability if you use a modem at home and have one phone line. Also, you can compose email anytime, save it, and send it later when you are connected to the internet. Email clients provide more features than web-based email, such as integrated spell checking which identifies misspelled words as you type, more powerful addressbooks, mail filters, and much more.
Email clients are generally much faster.
With web-based email, every time you click a link or button, you have to wait for the web server to generate the next web page and send the page over the internet. Email clients, on the other hand, are applications on your computer so the interface responds quickly to your commands. Some email clients allow you to check email and send email from multiple accounts all in one place. If you are using a computer at a cafe or library, you will not be able to use an email client. Yes, you can switch back and forth easily.