The ability to upgrade a customized system is a very important feature of Business Central. Most other complex business application systems are very difficult to customize at the database-structure and process-flow levels. Business Central readily offers this capability. This is a significant difference between Business Central and the competitive products in the market.
Complementing the ability to be customized is the ability to upgrade a customized Business Central system. While not a trivial task, at least it is possible with Business Central. In many other systems, the only reasonable path to an upgrade is often to discard the old version and reimplement with the new version, recreating all customizations. Not only is Business Central unusually accommodating to being upgraded, but with each new version of the system, Microsoft has enhanced the power and flexibility of the tools it provides to help us do upgrades.
We may say, why should a developer care about upgrades...