There's a myth out there that centering your content will make your text more attractive, and supposedly make the words seem more important....
However, from a visual stand-point, centering your content actually creates too many alignment lines in the layout. To make your site look clean, you need a logical layout that reduces alignment lines to as few as possible. The unpredictable centered content creates two irregular white spaces instead of one, which makes everything look messy. See below:
Can you see the difference in how easy it is to read this compared to the first paragraph in this article? You see the point. Centering content also makes it difficult to read. Instead of always reading from the far left, you have to figure out where to start to read on each line
When is it appropriate to center your content? Titles/ Slogans/ Short Sentences/ Menus, etc… (anything short and will be read quickly) are free game – so center away!