Most hikers will mail at least some packages to themselves along the trail and some use this as their only source of resupply.
Pros: You don't have to go shopping in towns. Your mailed box can better provide for your specific dietary needs. With your resupply box you can add maps and other gear that you might need along the way. Might be the only way to get food at certain resupply points.
Cons: Mailing boxes from your home address can get very expensive. You have to rely on someone to mail your boxes and add things you request before they are shipped. The bulk food you buy before the trip to fill all of your resupply boxes may be much more boring than you thought but now you are obliged to eat it. If you end the trip early you are left with tons of trail food. Post offices may be closed when you get into towns causing delays.
Buying supplies along the way:
It is possible to hike the entire PCT without mailing yourself one resupply box!
Pros: Often cheaper than mailing your self resupply boxes. Supports local towns along the PCT. No reliance on friends or family to mail boxes. Takes much less planning and effort than mailing boxes. You are able to pick and choose new food items based on your shifting palate.
Cons: Some resupply points are only gas stations or resort shops that offer little selection and may be expensive.
Before the start of the trail I will only be packing one resupply box to mail to the first resupply point, Warner Springs. Warner springs does not have a grocery store or a good place to buy food so it is an obvious spot to mail a package. After that, my resupply strategy will be a mix of the two described above. The difference with my resupply strategy is that I will build my boxes in towns that offer a good selection of food and then mail the boxes ahead to resupply points that don't. It will be cheaper to mail boxes from inside the state and I suspect I will only need to mail 4-5 boxes the entire trip.
I chose this method because it seems to make the most since for my budget and style of hiking. Some sections will go faster then I expected and some will go slower. By not relying heavily on mailing packages to myself I will be less tied to a strict pace.
With all of the PCT resources online it is pretty easy to figure out where you will need to mail a package. This is a good place to start. Craig's PCT Planner