With human error added into the equation, some defects are going to occur. If the tax function only has MS Excel to perform data transformation to make the data tax ready, the volume of procedures and controls will have to be significantly greater.
The problem is that in Excel altered data can lose its audit trail back to its source: mismatches with a companies ERP system. A point of attention as ERP data is the source of truth by the tax authorities (e.g. e-audits such as SAF-T).