IMHO, validation your codes is important for serval reasons. 1. It shows you client that you care about what you do and therefore you earn their confidents in you to continue to hire you. 2. It shows that you are know what you are doing. 3. I always put the two validator links (html and css) on my site. 4. When you show your portfolio to the perspective clients, they will trust you more if your codes are error free. (After all, would you want hire someone who's résumé that is permeated with typo and grammatical errors?) 5. In todays world, any Jacka$$ who knows a few html or css call themselves a web developer. By showing your codes are properly written, it make you stand out against the John Doe next to you. You are more Likely to be hired. 6. And for yourself, it is a sense of pride and satisfaction, you can be proud of your work. :)