The Graffiti alphabet is essentially the alphabet drawn in your own handstyle.
It’s not essential to draw the entire alphabet when trying to perfect your handstyle but like I say in my other posts regular practice makes for a more fluent style so it can’t hurt.
The idea of a graffiti alphabet is somewhat of a novelty in my opinion as to really get your styles down you only need to be working on the lettering combinations of your chosen alias. As I said still it can’t hurt to try the entire thing. You may find you find letters that interest you more than what you were working on in the first place.
My other thought on the whole graffiti alphabet thing is that if you are trying to create a digital font then doing a whole alphabet may be of benefit to you.
In terms of ustilising graffiti alphabets that you have seen on the internet. I would generally avoid, as simply someone has took the time and effort to create it, so you should too to create one if you are going to use it for your own ends. Also they can make nice canvases if you get the style you are after down nicely and finish it off with markers or some drip effects to polish it off. Plus there is a good sense of achievement in that.
So next time you peruse the internet checking out hand styles, make a note of all the things you like about which or try to replicate the sections of what you like about each one. When early tagging started to find its rise this was exactly what other writers were doing, finding things they liked on others and adapting it to their own tags to make it pop out. Avoid biting, see how you can utilise them to make your own style and hey if you wanna go the extra mile by all means try and test yourself and create your own graffiti alphabet to see how adaptive your new style is.