No. 1. They are light and quick. But you say "You need that mass.". Bologna (no offense bologna I like you). What goes forward must come back. That reminds me, my back feels a lot better using a wooden bench plane. I find I almost rock back and forth now instead of lunge and drag it back. I mean lift it not drag it. You will create a wear bevel on that back edge and mess up your clearance angle if you aren't careful. Now do you want that weight? I am guessing if you want more weight behind your plane then have some more desert.
No. 2. A blade that never shifts in use. I heard this surprise reaction over and over this last week at Woodworking In America while people tried out the wooden bench planes. I thought I was the only one that had this issue with the metal planes. I just really cranked down the lever cap to keep it in place and then it was so tight that the lateral blade adjustment lever was hard to make fine adjustments. I end up using a hammer for fine adjustments just like on a wooden plane.
No. 3. Fast blade removal and no cap iron to remove/reinstall for sharpening. This equals back to work faster coming and going. That takes me to no. 4.
No. 4. Never fearing I will strike my perfectly sharpened blade on the metal mouth while reinstalling the blade. I know I am not the only person that this pains.
No. 5. The ultimate feedback due to a solid connection the handle has to the body. Unlike a metal plane that has a bolted on handle that shifts in use, loosens because of use and, slight moisture changes a wooden plane telegraphs every subtle surface interaction with the cutting edge back to your hand. No need to see tear out, you know it when you feel it and intuitively begin to adjust your planing like the blind reading braille. Beautiful really.
No. 6. Never worrying about if you remembered to rub your plane down with oil so that it doesn't rust between uses.
No. 7. A lighter tool chest. Multiply that by every other wooden plane you have. Is your back feeling even better?
No. 8. Your Roubo bench no longer calls you a hypocrite. :) Ok that is funny admit it.
No offense to metal planes or there users. I have plenty of metal planes and they definitely find use in my shop. I have to say that wooden planes are hands down just more enjoyable to use. To me anyway.