Yeah I didn't explain that very well.

Say you have

G1 X10 Y10 Z0
G2 X20 R5 Z10

It will go smoothly from Z0 to Z10 along the length of the arc, so half way through it will be at Z5. Same as if you do

G1 X0 Y0
G1 X10 Y10

It won't do all the X movement and then all the Y movement, it will smoothly move between the two points.