I have encountered this situation twice recently.
One was a strip mall where the owner wanted to divid his largest space. This project became untenable, simply because of the work that would be required to separate / upgrade the electric for the new spaces. In building the strip mall, every trick had been used to keep the required meters / disconnects to a maximum of six - and adding the main disconnect that additional meters would have required in turn meant the wholesale replacement of the entire switchgear.
In hindsight, it would have been far better had the main disconnect been included at the start. That's what happens when you use the NEC as a design manual!
The other job was the opposite situation; I added a 'main' before just one service. Why? Because there are plans to add two more, and having the disconnectwill make the future work much easier to do.
IMO, a good design allows for future uses, and makes provisions for future maintenance work. While a good design is almost certain to meet code, a 'code minimum' design may be poor design.