I'll throw my 2 cents in here again as well (probably end up being 4 or 5 cents by the time I'm done though).

First of all yes, some people do measure thier groups. You are correct that the difference between 3.125 and 3.375 isn't a big deal, however if you are shooting 3 inch groups I wouldn't be worrying that much about it. That really isn't great shooting as far as target shooting is concerned. And fine tuning really doesn't shrink your groups, not in the way most think. What it does is makes them more consistant. Some top archers have shot some of the best scores recorded with really out of tune bows. The key was they had perfect or near perfect form.

Now if you can get bareshaft arrows, fletched arrows and broad heads all to group in the same spot (I'm talking 2-3 inches at 40 yards) then your bow is most likely tuned well and your spine is pretty darn good for your set up. Not to mention you have decent form and aiming skills.

Now lets say you get a bow and some arrows, then start tuning. Most will start will with paper tuning ( some will stop there[]). Then you decide to bareshaft tune, then maybe do some group tuning or walk back tuning. After you do all this you are happy with your set up and shooting the best groups you feel you can. And you are pretty confident the arrows are leaving the bow as straight as you can get them, especially if your bareshafts impact with your field points out to 30 or 40 yards.

Now you decide to slap some fixed blades on there. You shoot some arrows and they group fine but not where you aimed. Now you you want to broad head tune. In order to do this most will start messing with thier rest or nocking point. In essence changing what you were confident was a perfect tune prior to this. You may be DE-tuning your previous set up. Will you notice at 20 yards or so with field tipped arrow in your back yard? Most likely not, especially if you are shooting 3 inch groups on average. Now if you shot longer distances or indoor spots I bet your scores would change and your bow wouldn't be as forgiving anymore. I bet your broad head groups would also open up a bit as well. Would it be enough to make your bow so inacurate you can't hunt with it? I highly doubt it, I am quite sure it will be just as deadly. However I wouldn't count on shooting a 300 vegas round with it.

The reason behind this is most likely your arrow spine. Well matched and consistant arrow spine is pretty important in tuning and grouping well. Even more so with fixed blade heads.

It really boils down to what you want to do with your bow. Do you want an all around bow that will do both well? If so then broad head tuning is what you should try. I wouldn't even waste time on bare shaft tuning, just go right to broad head tuning and work on that until you are happy. The honest truth is that for most average archers well fletched target tipped arrows are pretty darn forgiving and if you have good form super tuning is not ultra important.

Now if you want a target bow that you will occasionally hunt with, but more than 90 percent of it's use will be indoor spots or 3-D then I would go for bare shaft and group tuning, then see where your broad heads impact and compensate for that when hunting. If you picked your spine well they should be pretty close anyway. If you tune your bow and your broad heads are 3-4 inches or more away from your field points something more is wrong then simple rest or nock adjustments. I'd start playing with the draw weight of your bow or looking at your grip and form.

Just my opinions anyway. It really boils down to what makes you happy and confident in your equipment.

Paul