[michaniskin]

Tasks in Boot cache their own products, so while the watcher task fires the rest of the pipeline whenever a source file of any kind changes, each task is smart enough to use its own cached compiled files. This is because only the tasks themselves can ever really know the relationship between source files and the compiled artifacts they produce.

So in practice things are only recompiled when they need to be recompiled. Even though the watcher task is firing, no real work is done unless it needs to be done.