Add docs on when ExecutionBlocker should be used

comfy/graph.py

@@ -208,6 +208,16 @@ class ExecutionList(TopologicalSort):
         return list(blocked_by.keys())
 
 # Return this from a node and any users will be blocked with the given error message.
+# If the message is None, execution will be blocked silently instead.
+# Generally, you should avoid using this functionality unless absolutley necessary. Whenever it's
+# possible, a lazy input will be more efficient and have a better user experience.
+# This functionality is useful in two cases:
+# 1. You want to conditionally prevent an output node from executing. (Particularly a built-in node
+#    like SaveImage. For your own output nodes, I would recommend just adding a BOOL input and using
+#    lazy evaluation to let it conditionally disable itself.)
+# 2. You have a node with multiple possible outputs, some of which are invalid and should not be used.
+#    (I would recommend not making nodes like this in the future -- instead, make multiple nodes with
+#    different outputs. Unfortunately, there are several popular existing nodes using this pattern.)
 class ExecutionBlocker:
     def __init__(self, message):
         self.message = message