From previous threads on this subject, I learned that it depends on how much height you need to add under the wheel to get your trailer level.
Adding a block to just one wheel gives you a height adjustment of 1/2 the thickness of the block. Under both wheels raises the trailer side the full thickness of the block. For example, if (like me) you're using 5/4 deck boards (they're 1" thick) to level your trailer, putting one under one wheel will raise that side of the trailer about 1/2". Putting it under both wheels will raise it about an inch. 2 blocks under one wheel, about 1-1/2"; 2 blocks under both wheels, about 2".
Your trailer's frame & suspension are built to take the weight (within reason). Just don't use your stabilizers to jack up your trailer. They are not
built to take the weight . . . that's why they're called "stabilizers", and not "levelers". Also, don't forget the wheel chocks
Hope this helps clear things up!