Spaces can also cause problems if you want to generate a URL for a username (requires inserting '%20') or if you want to generate an e-mail address for them.
Also, spaces (like dashes and underscores) make it easier to create similarly confusing usernames (i.e. "maryjane" and "mary jane")
Also, spaces (like dashes and underscores) make it easier to create similarly confusing usernames (i.e. "maryjane" and "mary jane")