why should I bother turning on my GPS device?

my Garmin says I did this

I actually did this

It looks like the Garmin decided to cut off my first five miles. Then it gave me about 5 more miles because of all the wiggling it thought I did while going straight up  the satellite bouncy Canyons of Broadway and 5th Avenue.

So the GPS makes it look like I started where I took a break to take a leak and then I ran 6 extra miles at a super fast pace so it almost worked out. N.O.T.