Yup. These are your answers for why Parcel is chosen a lot of the times. If the package isn't heavy or big though I don't see why Priority isn't the better option.
In my experiences, packages around 1 lb. going over long distances are cheaper with priority mail. Generally, items larger than 1 lb. get expensive with priority and parcel post becomes the way to go cost-wise.
Yep, it's a total crap shoot anymore as to what shipping will actually cost. If it's close, I go with Priority, but about half the time Priority is crazy (thought on rare occasion's Parcel has been the crazy one). I know there are flat rate boxes, but they're nuts. Looking at the chart, the medium and large boxes that used to run me $3 or $4 have quadrupled to $12 or $16 in the last 10 years. If you're selling on Amazon, where they charge commission on their grossly underestimated shipping stipend, you practically have to go with the cheapest option to stay afloat...
Bigger boxes cost much more for priority, so thats why I use parcel post most of the time. Just pack things extra carefully and you'll be ok.
I've bought quite a few items from the U.S and the shipping times between priority and first class mail is close to none and neither have ever arrived damaged, granted the seller does a good job of packaging. Here's a bit of info I came by that explains why people go either route: USPS parcel post is a ground surface offered by the USPS, and is estimated to take from 2 - 9 days, or up to 14 postal business days. Priority mail takes priority over parcel post and first class mail, is usually sent by air, and can arrive in 2-3 days, with a maximum of 5 days. parcel post accepts larger boxes/packages, while priority mail does not. Parcel post is a different service from bulk mailing, which is used by businesses who mail out large amounts of mail at regular intervals. Source: What is the difference between USPS parcel post and USPS priority mail
Everything I sell on ebay goes priority mail. The delivery confirmation has protected me more than a couple of time from scammers trying to claim fraud. Just recently had a woman buy something from me and claim her credit card was stolen and she never recieved the item. Delivery confirmation showed it was at least delivered to her front door, and paypal/ebay found in my favor. Every case brought against me I've won and I feel I have the delivery confirmation to thank for the greater portion of it. Coming up soon here, I have some large quantity items I need to sell so I may need to go parcel post on those. I'd like ot stay priority on everyting if I can, but I also don't want to be charging an arm and a leg for shipping either, considering I only charge the actual shipping cost. I don't do that BS, "I had to put it in a box and close it. Such hard work so I'll charge another $2 for shipping" that some people seem to do. And if I can, I try to offer free shipping or reduced shipping costs on more expensive items. I can live with paying for part or all of the shipping sometimes if it means making a customer happy.