Sometimes you need just to check how are some values in your application changing in time. Usually, you can use the log, but imagine that your application is on severs already and make the whole CI/CD cycle, just to add a few temporary log statements is overkill. Or variables are in 3-rd party libraries, and you don't want to patch it.
Of course, you can (remotely) debug your application, but it may be an issue to suspend the thread and check several variables again and again and again.
Such functionality is available in the JetBrains IntelliJ IDEA out of the box - tracepoint, but what about Eclipse?