Re: Why delay is a great effect?
I think it has many ways it can be used. I have a Boss DD-3 and i use it for many things. To make you sound fuller, emulate a reverb, to get some space ship noises.
At a short delay time (like 1-10ms) it can make the sound "dry".
You can do 50's Rockabily. I know some people doesn't like the digital ones to play this music but, i my opinion, you can get very sactisfactory sounds from them.
With a long delay setting (200-300ms) and distorsion you can make you solos sound great!
Just think of all the people and styles that have use them, well... In any style people have use the delay!
One of my favorites it is The Edge (U2).