Yep some trailers will have a swing-away jack. Generally speaking those are not supplied on enclosed cargo trailers or RVs.
Obviously there are exceptions.
But when you already have a trailer that has an a-frame tongue jack, and that jack will not go up high enough to clear obstacles when driving down steep driveways, backing over curbs, tackling rougher roads, whatever....then the Jack-e-Up can help solve some of those problems.
At my previous S&B, I HAD to buy and install one, otherwise there was no way to back my camper into the sideyard...because I had to literally back both the trailer and my pickup, up and over a curb that had a corresponding rise in the soil base beyond it...and my pickup's rear tires were backing down into the curb gutter. Meaning the factory mounting of the jack tube would make firm contact with the ground, causing damage, if I had continued.
With the jack-e-up, problem solved.
I think I paid $60 for mine...I see on the website they have gone up in price. No matter, if I needed another one, I'd pay it.