Most of people on planet use email accounts that come with their internet provider service for their personal email. These are included in price of service, so most people just use them because they don't know any better. I'd guess that outside of such services as AOL, WebTV and like, virtually everyone just uses an email client such as Outlook Express and their ISP's included email accounts.
When I began on internet, I simply used my AOL account to collect my email. It was simple (far simpler than just about anything else, actually) because is was included with AOL package. Once you set up AOL there was no configuration of any kind. You just used email browser and you were all set.
After I moved to Pacbell, I simply began using Pacbell email account that was provided as part of service. It's simple, after all, and better yet, it doesn't cost anything at all.
Later, like many people, I learned about services such as Hotmail, Yahoo mail and Excite mail. I got very excited, because these services solved several problems for me.
First and most importantly, by using my Hotmail account I could receive and send email from everywhere that had web access. While in theory I could do same with my Pacbell account, it was a hassle. Hotmail neatly solved that problem. True, web interface was no where near as nice as that provided by Outlook Express, but it was usable and convenient.
On top of that, as I began promoting my own web sites, I found that there are good reasons not to use your own private email account. I learned hard way, of course, by submitting my site to one of those FFA services and using my own personal email account address. I must have received 10,000 emails in a period of a couple of hours! All junk (the reason FFA lists exist is in exchange for a link list owner gets to send you one or more promotional email messages) and most even downright silly. Years later I was still getting an occasional email message as a result of that one mistake.
The next time I submitted to an FFA list (before I learned how silly these things are) I got a little smarter and opened a Hotmail account. All of email messages were directed to that mailbox, which I deleted a few days later. This saved me from getting tons of spam and wading through an incredible number of absolutely useless junk.
The final problem was anonymity. There are times on internet when not giving out one's personal email address is a good idea. I found email boxes at Mail.Com were perfect for this purpose. It requires only a few minutes to create a mailbox which is more-or-less untraceable. While I have not had any real use for this kind of anonymity, I mention it because it is one major reason some people use free email accounts.
Ah, but there are some disadvantages to using free email accounts. First off, ISP based email account's major disadvantage is simply that it is linked to your ISP. If you move or change ISP's, then you have to change your email address. This means changing every newsletter that you receive, every product update, notifying every friend and other person who sends you email, and so forth. Believe me it is a major hassle to change an email address.