Haven't washed my hair for 12 days. Bad?

I haven't washed the mop for 12 or 13 days now. It's greasy and matted a bit from wearing a toque but otherwise seems ok- no pain, excess dandruff, itch etc. Just wondering if this is bad or good? One friend said it was good because shampoo strips hair of natural conditioners etc. Another friend said it was really bad because the grease clogs your follicles and kills them. I don't know who to believe! Any thoughts?