Is it useful to install the sample data?

Well you are reading it right now! This depends on what you want to achieve. If you are new to Joomla! and have no clue how it all fits together, just install the sample data. If you don't like the English sample data because you - for instance - speak Chinese, then leave it out.

Newsflash

Joomla! 1.5 - 'Experience the Freedom'!. It has never been easier to create your own dynamic Web site. Manage all your content from the best CMS admin interface and in virtually any language you speak.