harmonic scales

Is it nescessary to know the harmonic scales --

Which scales are you talking about? If you mean harmonic minor scales then I think it's good to know them, it's very easy to learn them actually. I heard that harmonic minor scales are the most common minor scales, might be wrong though.
I highly recommend that you check Andrew's music theory videos if you haven't, at least the one about minor scales.

thanks for the reply i'm referring to the alfreds course book 2

I used the look inside feature on amazon.com and I guess you're refering to the G Harmonic Minor scale. Just check Andrew's video about natural, harmonic and melodic minor scales here:
https://www.youtube.com/watch?v=uyS9nqkeJe4

Just do the homework and you should know the structure of harmonic minor scales well (assuming that you already know the music theory he has shown in previous videos).

I heard that harmonic minor scales are the most common minor scales, might be wrong though.
I highly recommend that you check Andrew's music theory videos if you haven't, at least the one about minor scales.

I heard that too, but I personaly think that the natural minor scale is used mostly, music written in harmonic minor is scarce, well unless your talking about eastern music. However, heres one that is written almost entirely in harmonic minor: https://www.youtube.com/watch?v=fREuLCZd9SA
starts in major but changes to harmonic minor about half way through the intro.

I have just been practicing the five major positions on the guitar ( aka full scale down the neck ). I have to do the minor shapes too tho, but I got right onto the harmonic minor shapes instead, because being able to improvise arabic stuff is great ^_^

Do I think it's neccesary to learn? Yes...

How fun isnt it to surprice people, playing some ordinary stuff, and suddenly do an arabic riff.