When you customize software, you create more unique risk, and remove yourself from the pool of shared risk.
Shared risk is good, as there’s a good chance someone else might encounter a problem before you, and collectively you can encourage the vendor to fix it.
Selective unique risk is good because it can be a matter or method of differentiation for your organization. But unique risk, in enterprise software, is asymmetric.
Enterprise software is complex. You make a small change here and you see a large change there. You see changes in unexpected places, and in conditions which would have been perfectly normal before the change. When you customize software, you create new business impacting edge cases that no one else cares about.
So, if and when you decide to customize your software, remove yourself from the shared risk pool and create unique risk, make sure it’s damn well worth it.