The trailer is much more solid sitting on the landing jacks. Less shake.
When I was on the road and had to change a ruined tire the truck/trailer wiggles big time when a semi blast by at 70-80 mph out on the road.
Thats why I bought (years ago) a 12t shorty Truckers Special HYD bottle jack. It slides under the axle tube next to the U bolt. The jack has a slip on axle tube cradle so no axle slipping of the jack when the bow wave blasts hits the truck/trailer.
Now if I'm servicing all the axles then I park the trailer on the concrete pad in front of the garage and un hook the truck. Gotta' have the truck to chase parts or a tire.