Those files will be reuploaded to the server every time you update cPanel forcefully, so there's not much point to remove them. The better option would be to move mailman archives and the domlogs to /home with a symlink, which have been discussed how to accomplish in several threads on the forum previously.
Yes - and I have previously symlinked various directories to /home, where I have plenty of space. However, I then one day ran into a server crash due to some file corruption on /home. So, because the logs are constantly being written to, that scenario resulted in a substantially worse outcome than if it was not configured that way - the worse outcome being about 6 hours of downtime. Because I did not want to risk that scenario again, I reverted.
There is no real issue with being at about 81% on /usr or /var other than the fact that cpanel nags the hell out of you with warnings, which also then get texted to me daily.
So, last I checked, the 80% alert threshold was inexplicably hard-coded. That means that even though I don't care about being at 80% and would rather be alerted at perhaps closer to 90%, I can't do anything about it. The downside to this is that you begin ignoring the alerts because you are receiving them constantly, so one could end up missing the fact that a critical level might be reached.
As such, with regard to this very large directory of cpanel files, /usr/local/cpanel/src/3rdparty/gpl, if the only side-effect of deleting its contents is that the files would get recreated at some point, that is not a big concern. It's rare that I've ever had to do a forced update. As somebody had previously noted in this thread, it looks like there are several versions of certain binaries, so it is not clear if that is required or if cpanel is not cleaning up after itself and clutter is simply left behind to take up space.
The only consequence I could forsee of deletion is that if one then allowed the partition size to grow close to capacity, and THEN did a forced update, perhaps /usr would fill up entirely and something might bomb at that point in time.
If the recommendation, however, is to symlink a directory to /home, it seems more sensible to symlink *that* directory because it is otherwise relatively static and not being written to constantly like the log directories are.
What say you?