help to understand making process

[Dario Folliero]

i have two question:
first: in prmiitive mode with a disc selected if i put in view preference
Move Snap  = 1 (1/1000 LDU)
Rotate Snap = 1 degree
i dont have any change.

second: CSG seem dont make something if vertex is the vertex of the prim and the triangle are the mesh triangle. i think a make some mistake.

ok CSG intersection,i think i understand.  i do the same things with the internal disc?
ungroup primitive  and find the new intersection vertex?
i can delete some vertex or triangle?

apparently View-Preference dont have any effect only the Grid size works (yes i use ENTER and i select move o rotate button also). primitive mode and primitive disc selected.