1) What if you ever need to use the selector on a different element? 2) A performance hit (though so slight it might as well not matter) 3) Increased specificity
I have written a lot about CSS selectors:
http://csswizardry.com/2012/05/keep-your-css-selectors-short... http://csswizardry.com/2012/07/quasi-qualified-css-selectors... http://csswizardry.com/2012/07/shoot-to-kill-css-selector-in...
H