I haven't seen anyone post a reference to a manufacturer issued Owner's Manual, repair manual, engineering drawing, whatever, that shows the wheels should specifically be set to something other than coplaner. There were several references that they should be set coplanar. Seems pretty clear to me. Would I adjust mine if the saw cut fine but I found the wheels were not coplanar? Of course not, but I would and have when I had a saw that wouldn't cut straight until I did.
The teeth on a bandsaw blade result in that side riding differently on crowned tires than the back side. To compensate for that you have to tilt the upper wheel back a little. Different blade, different amount of tilt. It would completely unreasonable to expect that the wheels could be set in any particular alignment, coplanar or otherwise, and never have to adjust them.
I use my bandsaws for lots of things, one of them being cutting joinery on thick stock, think dovetails on something 4" thick for example. If the wheels are not pretty close to coplaner the blade will not sit perpendicular to the table. This presents two problems. First, the guides, including the thrust bearing, will ride closer or further from the rear of the blade as you move the assembly up and down. Second, the end of a stopped cut won't be square. Neither of these issues may be important to some folks. They are to me.
John