Gmail now has gone way beyond usefull , its now a necessity. They have 15 gb as free storage space , let me tell you that its a lot of space.
On almost all the other major platforms you can use the gmail credentials to sign up and login , it kind of convenient to do so because you dont have to enter the password everywhere.
The email client is great as well, very easy to use and user friendly. In terms of security as well gmail is very good , I would sugges to all the gmail users that have 2 step verification process in place. Make sure that you have that specially for the email accounts which has important and confidential information.
