I was initially listing a few examples of bad subjects, but removed them to not seem like I was picking on anyone, but I assume the examples are clear enough.
If your question can be summed up in the topic, that is great, and it will obviously increase the chances of someone reading what you write. If it cannot, then try anyway ;-)
Some made up examples
"Cool idea"
"Something to try"
"I wonder about..."
"What is this?"
"Strange planet"
whereas "When is the next update?" is actually a descriptive topic ;-)