Actually I was talking about the pre tt combination when used together. If someone knows how to use these tags, then when they're trying to represent a "code block" they'll "probably" use both tags together.
I agree that we should not give people gratuitous warnings about using tt or even pre, but a gentle suggestion when they're using both together would be IMHO useful.
In fact if you look at the post you were replying to, you will see that it uses tt tags. Sorry if my intent wasn't clear.