Yeah, the thing is as you distill you’re saving it bit by bit as you go along. You toss out the very first stuff (called foreshots) because it contains a number of chemicals with lower boiling points you don’t want (methanol, acetone, etc.) in higher concentration.

Then you get the heads, hearts, and tails and blend them together according to taste. You just wouldn’t get much separation if you distilled a small amount unless you were collecting in really tiny quantities.

So it just becomes harder to do a good job with a small amount.