Good question.

Ideally you would like the trailer to sit level. But the ultimate goal is to keep the weight on both axles close to the same.  If the front is elevated higher it can shift weight onto the rear axles.  If you are close to your tire/axle ratings, That shift can overload that axle.

It is not always possible to have everything perfectly blanaced. So I don't worry about small differences. If you have enough truck to tow the trailer. a small imbalance won't be a big deal.  If your tow vehicles doesn't dominate your trailer, being closer to being balanced is probably more important.

Newer model trucks keep getting taller. Manufactures keep putting bigger tires/wheels on the newer trucks. So older trailers seem to be going uphill when hooked up to a newer truck.