Selecting a piece of data within the stream shows you how it moved through the stream.
The other part of streams, for me, is that with the additional "each line does one, and only one thing" and you're not putting too much complexity in a single map, I feel that it forces you to write simpler code that doesn't need much debugging. The question of "how did that data get into the stream is where most of the debugging comes from.
I've found the stream debugger in IntelliJ to be very useful when looking at debugging streams.
https://www.jetbrains.com/help/idea/analyze-java-stream-oper...
The old plugin version of it has the same functionality (and better pictures) - https://plugins.jetbrains.com/plugin/9696-java-stream-debugg... (click the 'more' link)
Selecting a piece of data within the stream shows you how it moved through the stream.
The other part of streams, for me, is that with the additional "each line does one, and only one thing" and you're not putting too much complexity in a single map, I feel that it forces you to write simpler code that doesn't need much debugging. The question of "how did that data get into the stream is where most of the debugging comes from.