Despite the appreciation for standalone, client-based e-mail programs professed by Jeff Fox, Consumer Reports' Technology Editor (and I do use such programs myself), there are a few good reasons to use webmail—browser-based e-mail services such as Gmail and Hotmail— in lieu of or at least alongside a resident e-mail program.
Access from anywhere. Any Web browser, on any device, including phones and tablets, whether your own or someone else's, can connect to your webmail account, given the proper log-in credentials. Once you connect, you can read and respond to new mail, or your saved mail, which is kept "in the cloud" on the provider's server rather than on any specific device.
Better security. If your standalone, client-based e-mail program is set up to use a POP (Post Office Protocol, a standard method for retrieving your e-mail from an Internet service provider's server) e-mail account without encryption, which most ISPs allow as the default, e-mails you send and receive can be read by a hacker on the same network using simple, free software. Anyone logged into the same public Wi-Fi access point as you are can do this. As well, any government agency with access to your connection through your Internet provider (which does not require a specific court order anymore) could capture your e-mail transactions in plain text.
Webmail, on the other hand, like Facebook and Twitter, is almost always "scrambled" through an encrypted (https://) webpage, and it's very difficult and time-consuming to crack the 128-bit-or-higher encryption that's usually provided.
Stay safe online: FInd tips and advice at our Guide to Internet Security.
Reliability. If your computer crashes, your power fails, or your Internet connection goes down, new webmail can still be accessed over your smart phone or through a friend's or neighbor's computer. If you use an e-mail program on your computer, check with your ISP for their webmail-access site; for example, Verizon's is https://webmail.verizon.net. And memorize your ID and password.
Lack of spam. Most webmail providers have quite a robust and accurate anti-spam filter turned on by default. And there's typically a spam folder you can look through to make sure no desired e-mail got caught in error. Some e-mail client programs have anti-spam as well, as do commercial anti-malware programs, but they rely on spam-filtering rules stored on your computer that are not continually updated, as the filters used by webmail are.
Ease of switching PCs. Upgrading to a new PC is a chore in any case, and transferring an e-mail client program's saved folders and address book can be one of the most frustrating parts of the job. Microsoft tries to make it simpler with its Easy Transfer utility, but that works reliably only on Microsoft's own e-mail programs. Webmail doesn't live on a PC, so it doesn't need to be transferred.
If you want the best of both worlds, try using your ISP's IMAP e-mail server, if it's offered. That's an alternative to the usual POP e-mail that lets you use a favorite e-mail client for offline mail reading: It keeps the e-mail itself on a secure server, and when you're connected, it syncs the server with whatever device you're using.