I worked at a global multi-national telecom that used an ancient version of the software. You suffered with it. I'm convinced -- because we were always cash strapped (having been through bankruptcy and back) that part of the motivation for keeping it was that it made doing expense reports so difficult that many abandoned them.
SAP looked cool at the time[0]. The web UI had an appearance of a web app and attempted to behave like one. It had many flaws, but they all went unnoticed because of one massive flaw -- it failed to handle the Back button in the browser ... and the UI often put you in a state that "instinct" made you want to click it. When you did click the back button, the web app would see two of you. As this was not an allowed state for a user, the new "you" couldn't access the system until the old "you" timed out ... an hour later. This meant a sufficiently complex expense report could take two days to complete since, on average, hitting the back button (by accident) twice per line wasn't unusual. So if it resulted in less than $40 coming back, it often wasn't worth the effort to do the expense report.
My entire experience with SAP was limited to integration with downstream (simple) internal applications and expense reports. Others spent all day within it. It was bad enough to warrant a special launch page that popped the thing up in a window that lacked the back button[1] but that was a pretty inadequate solution.
The worst part was hiring SAP developers. Having not looked at the product since the mid-00s (and being far from huge-company-land), I don't know if it's still the case, but I suspect so -- SAP was basically a custom setup everywhere it existed. It had the same graphics, similar UI, but requires substantial development to tie everything into it and tie it into everything else. I ended up participating in the interview when the company "got serious" and decided to put some money toward hiring a solid SAP developer/lead to get everything upgraded and solve some of the worst problems we had. We brought on a guy and paid him 25K more than the highest paid developer on staff[2]. He, like the previous four (under-paid) employees, lasted about three months before he left for substantially more money. We tried "paying some third party", too. The problem there was similar -- whomever was contracted to us was either incapable of doing the work or didn't last long enough to get past initial planning.
The end result was SAP existed in our organization at the same version it was when it was setup, initially, until we got rid of it ten years later when we merged with a competitor. The competitor ran Oracle for ERP and had a team of people to manage/develop/maintain it. Personally, I'm not an Oracle fan, but I wanted to buy Larry Ellison a beer.
[0] This was the mid 00s.
[1] This idea, I think, was tried -- IIRC, the more frequent case was accidentally running into the Backspace key on a non-text field and having the browser hot-key back which isn't solved by taking the buttons away.
[2] This was saying a lot considering we had software actively developed in C++ that managed a pretty massive audio-conferencing service (and set of related bridges/hardware). I met with several on that team -- they were geniuses. The "SAP Guy" had to know Java and SAP. I interviewed him. I wasn't impressed.