We installed ceramic tile on our kitchen and dining room floor and did not seal the grout. About a month later, we noticed the grout was getting stained. (We have off white grout). I went to Lowes and purchased some grout sealer for about $7.00 a bottle. One bottle covered the whole floor. Anyway, I first cleaned the grout with a soap and bleach solution and after it dried, I then applied two applications of sealer. It was not that difficult or time consuming but the difference is amazing. It has been about 8 months now and my grout still looks new. Food and Juice do not stick to it at all. That is my experience, Hope it helps.
P.S. I used tiny little paint roller brushes (about 5 inches long) to apply the sealer, this seemed to work very well at getting down the grout line. I just put my finger in the hole of the roller and applied it right down the lines.