When they say "may vary", they mean by a fraction of a degree! Astronomers care a lot about precisely accounting for atmospheric refraction because if you want to look at a specific star or whatever, it kind of matters that you point your telescope in exactly the right direction. But for just pointing a solar panel roughly towards the sun, the simplified model from that site should be more than sufficient.

Only if the additional cost and complexity of such a setup is worth said cost. It can also be used to move the panels into approximately the correct location then allow the other techniques to fine tune it. If the more complex systems have a fault it may be possible to fall back to the more simple method which, while probably not as good, would be more efficient then just a static panel.