It's not that you'd necessarily want to use the ERP system as such. It just that many companies have base pretty much everything on SAP.
Perhaps you're a fields technician. Your assignments are managed by SAP, inventory is managed by SAP, the customer is managed by SAP, you, yourself is a resource managed by SAP. You venture out to fix a wind turbine, now you either need a laptop and remote in to enter things into a convoluted SAP setup and navigate the myriad of screen in that thing, or someone, perhaps SAP (the company) or some smaller company they bought attempted to bolt on a web GUI or a mobile app, as to simplify the work for the technicians.
There is an entire industry designed around building application to abstract away the SAP client and provide simpler interfaces.
Perhaps you're a fields technician. Your assignments are managed by SAP, inventory is managed by SAP, the customer is managed by SAP, you, yourself is a resource managed by SAP. You venture out to fix a wind turbine, now you either need a laptop and remote in to enter things into a convoluted SAP setup and navigate the myriad of screen in that thing, or someone, perhaps SAP (the company) or some smaller company they bought attempted to bolt on a web GUI or a mobile app, as to simplify the work for the technicians.
There is an entire industry designed around building application to abstract away the SAP client and provide simpler interfaces.