on the one hand.....
The main advantage of SAP is that 'it can be customised to do anything' (says sales person)
The main disadvantage of SAP is that 'it can be customised to do anything' (says CIO/CTO/Teccie)
The net result of the endless customisation over decades is systems that are vertually impossible to maintain and/or upgrade. Things get implemented becuase 'of course we can make it do that, Mr Business Exec' - without ever asking whether the underlying business process/logic make sense.
I once had the misfortune to be a tech exec responsible for a SAP system that had 'higher duties' allowances calculated three different ways within the SAME IMPLEMENTATION - which had been added to the decade long lifespan of the system (at that point)