The purpose of a taxpayer combination request (merge) is to delete multiple tax parcel numbers and create a new single tax parcel number for the combined properties. This is not a permanent action, it can be undone by a segregation request.
The combination action may not meet the requirements of a building or utility department that is requiring that properties be permanently merged. That merging can be accomplished by creating & recording a Declaration of Aggregation (aka Declaration of Single Lot Line) document, which contains language indicating that property will become and remain one total parcel. The effects on the property is that it is valued as one site, viewed as one site for building (if it meets building requirements) and that it would need to go through a formal subdivision process to be divided.
Below are a few examples of recorded Declaration of Aggregation documents: