A Parrot, while not strictly essential, does greatly simplify things but only on a stripping run
On a Stripping run you are collecting everything until the distillate strength goes down to 20% ABV or whatever your preference is. With a Parrot in place all you need do is swap collection vessels as the run progresses until you reach that point.
Without a Parrot you have to constantly take a sample in a trial jar and test it. Dropping the Alcometer into a collection vessel is not practical, especially with the Airstill, as the liquid level would never be deep enough to take it.
During a Spirit run a Parrot would be a liability and would make proper cuts virtually impossible - believe me I made that mistake in the early days -

Here's a pdf that shows the parts if you want to make one...
Parrot Parts List.pdf
Put simply, during a Stripping Run, when all you're trying to do is get rid of the crap in your wash, a Parrot does away with 90% of the drudgery and greatly simplifies the job
This pdf might help too...
Parrot Soldering Draw.pdf
This is one of my Parrots at work...
(click on pic for full size view)
...this allows me to collect distillate from separate Stripping Runs into the same collection vessel, in this case a DJ, because I can see the ABV as it drops, making Airstill Stripping runs less boring and more predictable
Simples
AM

Nice to see YHB back on board, your advice and wisdom has been missed around here
