Double Pitching

I see some recipes/videos where two packages of yeast are used. Without getting into complicated math and formulas, is there a simple general rule of thumb that tells you when you should double your yeast quantity? Is it simply based on alcohol content (more sugar requires more yeast to consume it).

Also, does yeast have an impact on resulting taste, aroma, etc?

TIA,

John

Use the pitching rate calculator. Adjust the growth factor to 0 if you don't want to make a starter. It will tell you how many packs to pitch. What it comes down to is that you shouldn't necessarily be doubling yeast for any specific beer. Rather you should be pitching the correct amount of yeast for every beer. That calculator generally will get you around 1 million cells per mL of wort per degree plato.

We also had a pretty good discussion in this thread about the same topic