I build my own scripts because I decide on what is needed and what is not needed as options for each package configuration, primarily for security and performance.
Yup; for me a major part was also thorough understanding of how the various parts of a working system interact.
Nowadays, few server admins realize that keeping e.g. server configurations in their standard locations is problematic, because it causes new related services to be "enabled" (if that is what distro maintainers have configured it to) by default when installed, and that can conflict with the existing configuration. My favourite example of this is Apache (the HTTP/HTTPS server). Many packages provide "utility" components accessible via the local server, and even in Debian, some of them are enabled by default. Personally, I move its configuration directory elsewhere, and require any new features to be added to the actual configuration by hand by an administrator. (Combined with admin action tracking even across '
sudo su -', this leaves an immutable log of which admin has enabled what additional features.)
One can be pleasantly surprised how much better performance one can get from an Apache or Nginx installation, with properly tuned settings and chosen modules. (The related security issues, especially using multiple user accounts per site, with server-side code unable to modify itself or create new server-side executables, is one of my
buttons I could rant about for hours on end.)
It is doubly important when you have a server with multiple sites, and user administrators of various levels (including students) and occasionally across subsites; I developed a well-working local groups based scheme with only a couple of helper utilities needed for that scenario.
At the time I maintained my own distro, around the turn of the century, one was a qmail mail server and DNS server/cache and NAT gateway for a subnet, and another was a file and print server for Mac OS (pre-X) and Windows clients, using Mars NWE and Samba, for sharing the same volumes. I did a lot of work around proper file locking (for MS Office users), but I cannot recall whether I got it bullet-proof or not. (It was good enough to not have issues I did not have workarounds for, though.) I had very good relations with the IT dept at that uni, but unfortunately my own stuff worked so well and I didn't advertise it enough that the dept heads had no idea what I did –– they just saw everything working as it should, with no effort... Started my own downfall, that.