I the past (and, almost certainly, the future), I spoke derisively about users who try way too hard to minimize mouse-clicks and feature count. While these things measure CAD gamesmanship, these things are never what accelerates a project.
CAD acumen is not tested by what you can make, but what you can change. Can your CAD models stand up to the twists and turns of unforeseen changes that inevitably crop up on the path from drunken marketing feverdream to final delivery?
What you speak of becomes so much more important when all files are part of the “Standard Parts Library” and have an unknown scope.
For me, the big slow downs have been in order from biggest to smaller:
In my experience:
…now back to year 5 of trying to get this global PLM system implemented. 
I wish I could like that post multiple times.
It is very true.
Makes me think of…
Engineers and Salesman.jpg
Edit to add: I was kinda surprised when I saw that meme in a SolidEdge blog: https://blogs.sw.siemens.com/solidedge/solid-edge-2022-user-perspective-design-configurator/
Interruptions by anything, or person… Stopping a train of thought and restarting again kills productivity.
Coffee Breaks! 
Superfast SolidWorks operators, creating SolidWorks files in huge numbers in less time. After that, small errors are included in the files, there is no way to change/reuse these files, all parts are made with surfaces, way to complex features and over weighted. And all these files have to be re-created. 
[sarcasm]
[/sarcasm]
Biggest slow down is hurrying up.
Useless meetings.
This.
People.
Meetings to prepared for the Meeting.
Ahh, the ol’ pre-meeting meeting. Yes…takes me back…
From a mold designer " Here’s my widget, go ahead and get started on the mold, I’m not done with the part design yet but I don’t think too much will change".
One person carrying the responsibility of 3 full time roles: design engineer, PDM/CAD admin, and 3D printing lead (I’m the only engineer)
Information bottle necks (or just no information)
Priorities shifting faster than the wind changes directions
Chasing shiny ideas for development projects
A broken PDM library (tons of out-of-context/broken references, out-of-band changes, assemblies released with unreleased parts, terrible check-in practices, little to no notes, etc.)
Me (8 months ago): hey, this is going to be a problem, but I have a plan on what we need to do to fix it
{no one cares}
Sales (2 weeks ago): THIS IS A PROBLEM WE MUST FIX IMMEDIATELY
{now everyone cares, but only enough to figure out convoluted work arounds to have ‘sales ready’ drawings}
Maybe I’m too much of an idealist, but I’ve seen so much of the above, I’m starting to worry that I’ll see so much more of this no matter where I go next…hopefully someone can tell me it’s better some where.
Recently been getting a barrage of emails from a certain CAD vendor telling me their software will make projects go faster.
No, honey, It won’t.
Another project timeline killer–adding or losing people.
Adding people can be worse than losing people.
Manager: “How far behind are we?”
Engineer: “Six weeks.”
Manager: “What if we add two more people to the team?”
Engineer: “Sixteen weeks!”
I’ve repeatedly told the higher ups here that it would be more cost effective to pay people to sit on their hands for 6 months if we have a slow down. Laying off/letting go people who know what they are doing only to hire people who don’t six months later is madness.