Many things can be approached with simple and direct ways including business and especially business. We have enterprise resource planning, our very own SAP to make business more accountable, less prone to human errors and therefore easier. The integration in SAP is what makes it much sought after, whereas thorough dependencies and good standard reports make it a business savvy product.
Nevertheless, Z-developments attract companies, organizations and individual users to an amazing extent. It can be attributed to business needs, custom requirements of each industry and business vertical; which can definitely be addressed with Z-developments in SAP. And some of them are absolutely essential to allow for uniqueness of a given business and to create value for the users.
That said I have come across users who do not want to go to multiple transaction codes in standard SAP to create subsequent documents. They expect a single window where many buttons will create multiple documents and the zapping part is that they do not want to see the created document. Well, when SAP was not there, documentation still happened and nobody ever expected not having to see a document they were creating!
The maintenance of these Z-developments is time-consuming and expensive to say the least. Imagine the scale of expenses both operational & financial on both sides of business. Each time there is a change in personnel; huge time has to be spent on training and user ease for these multitasking Z-developments. 
Each time a new business scenario is mapped in the system, apart from standard configuration and Z-screen; ten other Z-reports have to be revamped to accommodate data from new scenario. While it seems good business for consulting, there is no actual consulting involved where simply individual user wants are accommodated, with no regard to overall business & core activities which the software was intended to support.
ERP must be used to simplify & standardize business documentation while allowing for focus on core business competencies and the same must be the goal of consulting & consultants. The whole idea is to not forget the underlying simplicity of processes & maintenance while looking at the overall complexity which is but a result of various simple processes linked together to create something of more value.
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