You can whiten your teeth at home and do a pretty good job with home teeth whitening products but having your teeth professionally whitened will do a much better job.
I still whiten my teeth sometimes at home but sometimes I will go in for a professional teeth cleaning and teeth whitening procedure and it does work better and well worth the cost.
You don't have to do it often and if you can afford to have a professional teeth whitening procedure done then I highly recommend having it done.
The dentist who whitens your teeth has better ways and products to whiten your teeth with that does a better job than home teeth whitening kits.