Like with most things, context matters. If you have a "closed" system (such that "you" control the database, and all access to it) then upgrades are "easy" to

Like with most things, context matters. If you have a "closed" system (such that "you" control the database, and all access to it) then upgrades are "easy" to do. You just upgrade the server and all clients. If your system is more diverse then it's harder because in that case server and clients gave to be upgraded together. If I'm using multiple different programs (Accounting, Payroll, Access control etc) possibly from multiple vendors, then coordinating everything to happen at the same time can be impossible. If the server is not backwards compatible with old clients then you can get stuck. In the case of SQLite for example lots of systems rely on the stability of the file format. Breaking that would not be welcome.