its a mixed bag. i went straight through, and on the whole i don't regret it, but there were times when i did.
you miss out on what could probably be some very fun experiences. it seems nice to have a job you don't take that seriously and take time to just relax and think about your life.
you lack real world experience that employers might value.
you will be less worldly than your peers and feel less cool.
depending on the person, you may be burned out from undergrad and not work up to your full potential.
you are still in the academic/study mindset while many of your peers are used to never working on nights or weekends.
you get it over with. in a few years, when your friends who took time off eventually go back to school, you will already have finished and started a career.
if you know you want to go to law school, anything you do in the meantime will probably just be killing time and you might find yourself with more interesting opportunities once you have your JD.
it's a close call that depends a lot on the person. there will probably be times when you regret going straight to law school, but overall it probably evens out.