This is sort of a big deal. Apple is, without your consent or any warning labels, logging all of your iPhone’s location data and then transferring it over to your computer when you backup or sync your iPhone. The information is easily accessible — unencrypted and in a standard database format. (The option to encrypt is there, though I haven’t tested whether this option obscures your location data.)
Upshot? Any program you install or anyone you let on your computer could access this data, giving that program or that person full access to where you were and when you were there.
This person drove from Winnipeg to New York City. Had a weekend trip up to Montreal to visit friends. Spent most of the time in New York City.