For the Vector skin (the new default skin in the English Wikipedia as of May 2010), this style limits the width of an article, so maximising your browser window won't produce lines too long to be readable. If the browser window width is reduced, the article width still follows the window.

Note that the "after" screenshot shows the effect of my three Wikipedia (Vector) styles combined. The changes for this particular style are highlighted by the right caption.

[Screenshots in grey to save space.]

The other styles shown in the "after" screenshot:
• http://freestyler.ws/style/24747/wikipedia-vector-compact-top-change-title - compact top, change title
• http://freestyler.ws/style/24749/wikipedia-vector-old-logo - old logo

Also available for Vector:
• http://freestyler.ws/style/24804/wikipedia-vector-expand-languages - expand languages