Wow, your question must have resonated with a lot of readers, as the "hit" count reached an all-time high for the Sunday forum, and I see many have returned this morning to see my answer.
Let's say you're working with aromatics that are thick, like labdanum, or a concrete. You're also working with aromatics with a thin, watery consistency, like blood orange or lavender. A lot of absolutes are thick, and also quite pricey.
The first things my student learns to do is to dilute the aromatics, both the thick and the thin, in alcohol to a 10% dilution. That's 10% aromatic, 90% 190 proof alcohol.
Using uniform droppers, without squeezing the bulb, but instead applying gentle, consistent pressure, they practice making accords with the diluted drops. The only way they've used the scale so far is to measure the bottle, alcohol and aromatic. And added bonus: that expensive jasmine grandi or orris is stretched further in your budget. I couldn't image using 100% expensive drops! Plus, the alcohol "opens up" the aromatic, showing its true scent profile.
Granted, for the final perfume they submit, they're using drops. Maybe 15 drops of this, 10 of that, 5 o another, maybe 2 of an accessory note, 10 more of another, etc. Nothing crazy like 100 drops of a thick, undiluted material, never!
For Intermediate and Graduate level students, they learn about specific gravity. Using the SG of an aromatic, I have a software program I developed that allows them to convert the diluted drops into undiluted aromatic, which they weigh out in grams to reproduce a perfume, at any concentration, and at any amount.
Long answer - a professional perfumer must use a scale. It elevates, simplifies and brings precision to their work.
I'm a rather strict Instructor: I hold my students to high standards as they progress to become active, professional perfumers. I do not accept students who wish to begin a perfume business right after completing the course, with rare exceptions. Perfume study takes years of experimentation, and the perfumer must challenge themselves. Learning the basics in the most correct, systematic manner is what I educate them about at http://PerfumeClasses.com