hey! I'm just gonna boost this with a comment. The issue is because AE was made before multi-core computers were really even popular, let alone GPU's. it was made in the time where there were even RNG (yes random number generator) cards.
also check out https://adobe-video.uservoice.com/forums/911311-after-effects/suggestions/44254728-stop-adding-new-features-till-the-program-works-at for my latest post. lets get these performance issues addressed, even if it means trashing the program for an all new one.

Clicking and dragging a keyframe to then not have it move, then jump forward a couple seconds later, is super annoying. It makes it really difficult to work quickly.

Oh look! I built a new workstation! (Specs: https://pcpartpicker.com/user/Cx/saved/gWRk99 )

What's amazing: Cinebench scores are fantastic! Lowest rendering time (quickest!) of the many years I've been running the AE Total Benchmark scene! Everything else I run other than AE is much improved!

What's not amazing: AE previews are still slow and the UI is laggy. And there's seemingly nothing I can do about it.

PugetBench results: Overall score of 1156. (The School of Motion article listed in the response from Victoria Nece shows a score of 985.)
https://www.pugetsystems.com/benchmarks/view.php?id=8834

CPU-Z benchmark results: 16336 (multi thread) / 499 (single thread)
https://valid.x86.fr/bench/mdpwvq

I am beyond frustrated at the state of this application. It is, without hyperbole, the greatest pain point in my professional life.

What really slows down the overall UI including Composition Footage Layer Window, Timeline, RAM Previews, Text Tool (Selecting text and Editing), Shape Layers, Activated Rulers & Guides, Panning in zoomed in Composition Window, drawing Masks, Painting etc. is when in Preferences -> Display:

"Hardware Accelerated Composition, Layer, and Footage Panels" is activated!

Especially when working with large footage files and compositions (4K, 8K).
Turning it OFF in Preferences speeds up everything although I have a nvidia GeForce GTX 1080 board which should be more then capable to accelerate AE's UI.
It should be the opposite (turning it on) but it's not!

Adobe is still very bad at using the GPU properly and this GPU UI acceleration never worked for me on any computer I worked on regardless which CPU (AMD or INTEL) or GPU. I always turn it off for performance reasons for the good.

Turn it OFF and enjoy a much more snappy overall UI ;)

My System Specs are quite fast but Adobe is still crawling:
AE 2019 16.1.3 (Build 5)
OS: Windows 10 Pro 64bit
CPU: AMD Threadripper 1950x (16 Cores @ 3,6 - 4,2 Ghz Turbo)
GPU: nvidia GeForce GTX 1080 8GB StudioDriver vers. 431.70
RAM: 32 GB G.Skill Trident Z Quad channel DDR4-3200 CL14
System Drive: Samsung NVMe M.2 SSD 960 EVO 512GB
AE Cache Drive: Samsung NVMe M.2 SSD 970 PRO 512GB

I can confirm that deactivating "Show cache indicators" massively improves UI refresh during previews. It's utterly absurd, and should be fixed too, but good to know.

I am also very unhappy with the responsiveness. Maybe a solution could be to be able to switch the UI-Design to a simplified but more responsive Version? If you use the Newton Plugin (by motion boutique) you never experience even the slightest lag no matter how many layers you stuff into it. I always wonder what's the big difference here.

I assume it is not only about of screen resolution or Ghz. The question is what happens during the selection of layers? I believe the Application reads out the information about keyframes and expressions or whatever you are selecting. Only when finished it allows the screen to "go on scrolling" an "show the selected things as selected". I am sure there is a way to unlink those two things? Just let me select and move stuff quickly. I don't mind when it takes more time afterwards.

This is actually about the users health. If you experienced ellbow or shoulder problems due to computermousing you'll know what I am talking about.

Yes please! I suffer SEVERE slowdowns on playback on a 4k screen on W10 and a threadripper, just because of the timeline updating... if I make the timeline smaller I can gain maybe 10 or 15 frames per second. It makes playing 60fps footage impossible in real time.