Regression testing of SAP changes is a bit like flossing: everyone knows they should do it, but in practice, it’s something that only gets done sometimes, and usually not very thoroughly.
To stretch the metaphor further — everyone knows substandard flossing can have nasty results, maybe even the loss of a tooth or two. It’s the same with regression testing: everyone knows poor coverage means defects can slip through into production, causing errors and downtime in business-critical systems.