With Spring Core (the DI container) the only parts of your code that have to depend on Spring are the config and your entry-point.

You can choose to import facade-style Spring libraries, and write your code against them -- like Spring JDBC, Spring JMS, TaskScheduler -- if you want something that does some heavy lifting for you, but doesn't tie you to a vendor implementation directly.

Meanwhile, Spring Boot is a fully-opinionated framework based around the combination of defaults and on-the-fly auto-configuration, and giving you a single runnable uber-JAR at the end. And you're right about it: if you're using Spring Boot, it makes sense to depend on other Spring libraries, because (1) the docs guide you into them, and (2) the two will interact to auto-configure. For example, you can just run your DB code, and it can auto-configure an in-memory instance as you're developing [1]. Then, when you've gotten the real database, just specify the real config.

Spring Boot really shines in bootstrapping a greenfield project to get going quickly, especially if you're willing to compile its annotations into your code. You can then go back and incrementally override behavior and configs once you realize you want them a certain way.

[1] https://docs.spring.io/spring-boot/docs/2.2.7.RELEASE/refere...