ERP systems or Excel

ERP systems simply don't align with the needs of the business.

1. Many ERP systems don't allow you to see forecast and actual customer orders in the same view.
2. Many ERP systems have an "all or nothing" approach to capacity planning – you need to fully populate capacity planning data and track actual performance at the operation level or you can't do capacity planning.
3. Some systems only present views on a part by part basis – so you can't see aggregated details without running a special report
4. Most systems make it very difficult to try what-if scenarios and get timely results.

There are many more examples, but what is interesting is what happens when ERP users don't get what they need from the ERP system; they try to get the information someplace else…typically from Excel.
I've talked in previous posts (How are spreadsheets like cockroaches?, Is Excel the right tool for S&OP?) about the dangers of running your business on Excel.  Excel is a fine tool for creating charts and doing one time analysis, but things start to fall apart when you start building business processes on it. Like a foundation for a building, the software you build your processes on is critical.  A weak foundation, and your process will come tumbling down. So why is Excel a weak foundation?

• Excel propagates multiple copies of "the truth". How many times have you gone to a meeting where two people presented different versions of what is supposed to be the same data?  Whose data do you believe?
• Excel allows non-validated business logic. Who created the spreadsheet? How sure are you that the formulas used are correct? In my "How are spreadsheets like cockroaches?" post, I cited a study that showed that 90 percent of spreadsheets in use by businesses today contain serious errors.  Errors that could result in you making a bad decision.
• Excel has a poor collaboration model. Many processes today require inputs from multiple people.  Excel doesn't handle concurrent edits well, so often processes must be structured such that edits happen consecutively. This can prolong processes, especially if you have difficulty getting people to make their changes on-time.
• Complex processes result in complex Excel worksheets. I managed the S&OP process at a manufacturing company in a previous life.  The S&OP spreadsheets for our four product lines were built up from multiple component workbooks.  Macros were used to manage the rolling time window. When something went wrong with the process, I was guaranteed to spend days trying to debug and pick up the pieces.  Things went wrong far too frequently.