"close" counts in horseshoes, handgrenades, and dish alignment
If you try to align on a bird that's 30º off true south, you'd better better have a darned good reason, and lots of experience!
I think that's because its just easier to deal with as far as skew, most folks get confused with skew before they figure out that the motor does it for them...
So, if you are aligning on a satellite that's 5º (or maybe 10º) off your true south, the apparent mis-aiming and skew won't distract the user too much.Also, because of skew, an offset dish it is hard to figure out just where it is aimed by looking at it.
If you try to align on a bird that's 30º off true south, you'd better better have a darned good reason, and lots of experience!