Yahoo Mail now, finally, offers a constant HTTPS connection. Sadly, it is not (yet?) switched on by default for most cases. Happily, it's easy to switch on by hand.
Should you do it? Yes, you should do it. Especially if you access your Yahoo Mail wirelessly, and particularly, if you do so from public wifi hotspots. Even if you only use your Yahoo Mail once in a while. Just do it now. Won't take but a minute.
Unless there is something truly pathological about your computer set-up, you should notice no difference at all, except for the appearance of a lock icon in your browser's address bar, as shown above. Things aren't going to get noticeably slower, you won't need to type in extra passwords, etc.
What is HTTPS? Basically, it's a more secure way to connect to a Web site. When you visit a site whose URL begins with
https:// instead of plain old
http://, information transmitted between your computer and the site is encrypted automatically before being sent. This makes it virtually impossible for someone else to eavesdrop on you. More details (than you probably want) are available on Wikipedia.