Having broadband changes the way you use the internet. From downloading anything to uploading files, checking emails, to online banking. The fact that its always there makes it much more of a useable resource. It can integrate much more into your normal life.
The saving is if you are on a 2nd phone line already - broadband gives you your phone line back for phone calls.
You don't have to waste time connecting (lots of times a day soon mounts up!) or worry about leaving it on for long periods. If you can afford it go for it, but accept its a luxury more than something you can't live without.