I've believed that the best cutting edge is achieved when we sharpen plane blades to a mirror polish.

I understand that this level of honing is important on card scrapers and smooth planes where you are trying to leave a surface that is ready for finishing.

However, for roughing work - like on a jointer or jack plane blade, is it really necessary (especially when you plan to follow up with a polished smoother?)

I sharpen my lathe tools to a scratchy 80 gt, and they cut just fine. I was sharpening a jack this morning and started with 150g, got distracted, and forgot to hone before I reinserted the blade into the body. It cut fine.

In fact, might edge retention be better on a coarser honed blades?