When buying that ERP solution, you have your current processes which have to be mapped to the processes capabilities of the Module which you buy. So you may be doing the process in one way in your organisation whereas the Module which you buy may be doing it in a different way, which the selling company may propound as the best practice and ask you to switch to that way of executing the process. The difference between your way of working a process and the way software does it is called the GAP. For example if 70% of processes match then there is 30 % GAP. This GAP can either b efilled by customisation, butn no company offers you 100% process match. So it is up to your wisdom to decide how much GAP is acceptable.
What ever the GAP is , that much change has to take place in the organisation and as you know that any change entails, resistance and a cost of training and build up. Hense it is pertinant to close the GAP as much as possible. If the GAP consists of an actual industry beset practice then adapt it as it will add to the bottomline. So the best is left to the descretion of the task force.