So I am doing up my glow plugs and injectors (save that for another post(s)), and I decided to take the slack out my throttle cable
And as I am taking the slack out of the second cable (with orange boot below)

, I have to ask myself, what is this cable for? and should I be taking slack out of it? What am I adjusting? What should it be adjusted too?
anything else I should be adjusting while I am in there? read some posts about upping fuel pressure a bit? (what is the adjustment, how much?)
Comments? // Advice?
Cheers!