The answer of this question is really an ideological dilemma, every user has his own reasons, but among the most common causes,

* place a CV or a Portfolio online.

* Place an online photo gallery.

* Use the web as an Electronic wide spread Business card.

* launch a personal website (singers, artists, Djs', Advocates, and other professionals).

* launch an online community.

* launch a News management and delivery system.

* launch an online front for a Shop or another business.