If the bearings have been properly greased by your shop, then no reason to just shoot some in. It isn't like the bearings lose grease.
The thing is, you really do not know what the shop did..
On EZ lubes, you can't just blindly shoot grease into the fitting, there is a procedure that you need to follow.
You must rotate the wheel while adding grease via grease gun. Failure to rotate the wheel can result in grease pressure building to the point the grease pushes out the inner grease seal and then it ends up on the brake shoes.
That means you need to lift each wheel off the ground enough to be able to turn it while adding grease.
Turning the wheel while adding grease allows the grease to push through the inside bearings easier, back into the spindle to the outside bearings and then you should see grease push through the outside bearing.. Once that happens you can stop adding grease.
If the shop never used a grease gun, then the inside of the hub won't have much grease and it can take a lot of grease to fill the void the first time.
I personally don't care for EZ lubes they waste a lot of grease and makes servicing and inspecting the brakes a real mess and chore to do.. I don't personally use it as I have one trailer with and one trailer without and simply remove the drums, inspect and clean bearings once every two yrs. One small container of grease lasts me many yrs and I use a lot less rags.