Being able to swap things out is one way to make a framework lighter.
Light ones: if I have a problem with the framework, I am guaranteed to have a local solution without getting rid of entire framework. For example, if Spring Framework does not let me create an object in a particular way, I can write my own function to create the object. If the way configuration is being located does not suit me, I can replace the mechanism without getting rid of Spring Framework or even configuration -- just by implementing couple of interfaces.
Heavy ones: if I want to do something that has not been planned for by framework creators I can potentially run into problems that I have no way out of without getting rid of it all.
An example would by systemd: it is built in an unnecessarily heavy way by insisting on you using it all. For example, if you don't like journald or can't use it for some reason -- tough luck. The only way to get rid of journald is to get rid of entire systemd.
Light ones: if I have a problem with the framework, I am guaranteed to have a local solution without getting rid of entire framework. For example, if Spring Framework does not let me create an object in a particular way, I can write my own function to create the object. If the way configuration is being located does not suit me, I can replace the mechanism without getting rid of Spring Framework or even configuration -- just by implementing couple of interfaces.
Heavy ones: if I want to do something that has not been planned for by framework creators I can potentially run into problems that I have no way out of without getting rid of it all.
An example would by systemd: it is built in an unnecessarily heavy way by insisting on you using it all. For example, if you don't like journald or can't use it for some reason -- tough luck. The only way to get rid of journald is to get rid of entire systemd.