I personaly have ALL my tires balanced because of bad experience of not having them balanced. A few years ago I had new tires installed on my bass boat trailer and the tire salesman talked me into not having them balanced, he said I didn't need to on a boat trailer, now these were 14 inch tires.
Well we live in Ohio and I was going to a bass tournament in Florida, it was appox. 1,000 miles one way or 2,000 miles round trip.
Made it down okay, didn't look at the tires when I got down there. On the way home about 100 miles from home stopped to get some lunch I happened to look at the tire on the trailer, got the shock of my life, it was "cupped" across the tire so I walked to other side and it was the same way.
When I got home I took the trailer to the tire dealer and had them look at the tires, the salesman said "Gee, guess you should have had been balanced and that wouldn't have happened." Well we will sell you another set.
Well after I said a few words that weren't nice, I told him where to put those tires and I would never buy anything from them again.
I went to another tire dealer, he looked at the tires and said that he always balances all the tires he sells just for that reason.
Some people don't drive there trailers very far or long so they can get away with not balancing, but it's common sense to balance for safety, less suspension wear, longer tire life and $$$$ saved on buying tires.
So, that is why I always have tires balanced.