Couldn't we just store data in Excel? Yes, we could, but there are some problems.
In Excel, records can be edited directly (without script) and mistakes can be made.
In Excel, data isn't accessible by users throughout the organization unless the file is shared. But, if the file is shared, anyone can edit the data and alter the database for all other users.
Excel is best used for data analysis not data storage.
Data integrity refers to truth in data, or how the data present the truth of the underlying transactions or events that occurred.
To be most useful to decision makers, accounting information must be both relevant and be a faithful representation (free from error, complete, and neutral) of what occurs.
Having a centralized database prevents the organization from having "multiple versions of the truth," where different users all have different versions of the data, some versions more up to date than others.