Is the expression "may or may not" semantically void?

I personally have a hard time accepting the use of "may or may not." To me, it seems as if "may" and "may not" effectively cancel each other out, so the semantics of the sentence in which it appears are no clearer:

I may go to bed early tonight.

This seems to indicate that it is likely I will not go to bed early tonight.

I may not go to bed early tonight.

Contrariwise, this seems to indicate that it is likely I will go to bed early tonight.

I may or may not go to bed early tonight.

This seems to leave me with absolutely no clarity as to which eventuality is likely to occur.

Am I missing something obvious here, or is this particular expression just a rhetorical device for saying, "I'm on the fence?"

"May or may not" is used to indicate that the point is under thought or scrutiny. It's not meant to give a clear indication that one option is more likely than the other.

For what it is worth, you're not alone in your difficulty accepting the phase. I usually follow up use of "may or may not" with one of two statements:

• My understanding of the situation remains unchanged.
• Let me know when you figure that out.

You could say you may or may not do something if you wanted to emphasize your undecided state of mind.

I may or may not go to bed tonight.

This lets people know that you have a decision before you. It is not a "nothing" statement. It is commenting on your state of mind.

I may go to bed tonight.

This announces that you are considering going to bed. It may also be said ironically, if you are being kept up quite late and think you may never get to bed given what you are doing.

I may not go to bed tonight.

The announcement here is that you are considering staying up all night. This would probably not be used ironically, since it is unremarkable to consider the opposite of not going to bed.