It makes it simpler for police and three letter agencies to gain access to your dna without needing to go through proper channels. It is how that famous serial killer/rapist got caught on a 30 year old cold case.

I know the response is "Well I ani't killing/raping so it doesn't matter."

A lot of people have been sent to jail on false positives on dna results. It takes to much time to actually compare a large chunk of dna so they select certain parts to compare it to and if you fall into the unlucky percentage then you are screwed.