If you do that (not including a newline inside the code tags), it means that your code doesn't wrap as effectively and it gets downloaded as a comment.

If you instead, as frodo72 notes, include a newline inside of the code tags (for example, at the start and/or the end of the code), then the displayed code will be enclosed in P or PRE tags, depending on the viewer's settings. Wrapping your own P tags around such shouldn't be done.