I tested early as I wanted to see if I could use specific treatment for thrush, and when I got a BFN I thought, 'Oh well, I knew it would be arly to test'. (although lots of other women on here have had their BFP on 12DPO!)
However I had specifically bought a twin pack for that purpose so I wasn't too annoyed with myself. Got a BFN but decided not to use the tablet anyway just in case.
2 days later I got my BFP...this was also before my AF was due, and TBH if I had seen a BFN I would have been annoyed with myself for not waiting.
However, sometimes you just got to know, even if the result isn't the one you want to see....