I always practice one way,,,,, offhand! I test and sight-in on benchrest, and use the best benchrest equipment when I am testing to eliminate every little human error possible. This includes the use of windflags!! Trust me wind will cause more errors in POI than most will see by not using a level!
I have over 30 years experience in benchrest competition, and can assure most shooters they don't have a clue how detrimental even a 5mph wind can be to their shooting, even from a rest, but magnified offhand, and shooying offhand for practice with a couple flags will improve your success in the field. The more you practice this way, the more you will see improvement when it matters!
Variable wind cannot be seen in most cases without windicators of some kind, and guessing wind by how it is hitting you is of little good, and can be totally false to what it really is. check out this 5 25 and 40 yard variance and you can see, wind swirling from 3 different directions.
From one shot to the next, this can be giving two totally different POI using the same POA! Throw in this scenario and 3 different Points Of Impact using the same Point Of Aim would be tr results, the higher the wind speed, the wider the spread!
I also have owned some bows that shot to a different POI when shot offhand, than they did from a bag. One thing I have never had to deal with using the Excalibur bows, and the easiest of all for me to shoot offhand was my Suppressor, and Micro, mainly because of balance, but all my recurves have kept their zero when shot offhand very close! My Matrix 380 might shoot 1/2" low but out to 40 yards, the max I will shoot in the field offhand is still deadly accurate with or without a rest!
Since I use preset reticles and don't rely on twisting and adjusting on the go for every shot, that 1/2" is less from 20 to 40 yards, and beyond that not an issue as I do use something for a rest, from bracing my back or forearm to using a rail or shooting stick's which I usually use as I am mostly on the ground!
I just shot the Mad Max 2 days ago, for practice,,,, only 2 shots, only 30 yards, one with a broadhead, one with the 125 grain Viper Trick, 90% of my practice is with the heads I hunt with, and always the same set of arrows I currently built for that bow.
Pretty much same POI both shots, so again, my choice of fixed blades prove to hit where my field tips hit, and both withing 1/2" of where I was aiming. I said earlier, this does not matter past 40 yards in on live game, as beyond that.
I have confidence in my ability, but confidence is not 100% positive, and past 40 I will take the right shot if the right animal presents it, but the farther out I get, the better that rest would have to be, as well as the conditions, whish is everything from light to wind, and cover!
But anyone who doesn't practice off hand, will never be efficient offhand! You may not shoot satisfactory to your liking in the beginning, but in time, anyone can and will be a much better shot if they just stick to it, and concentrate on the spot you aim at, slowly squeeze, and concentrate on following that arrow all the way to the spot you are aiming at!
But please, give the wind indicators a try, and see if it doesn't explain a lot of the shots that aren't where you want them, or at least part of the reason they are as far off as they are. This to the more you use and concentrate on what they tell you, will help prepare you for conditions you take for granted in the field! remember, head and tail winds can lift and drop shots as well, and helical fletched shaft can lift as well or drop in cross wind as well as drift depending on if they are spinning into that wind or with that wind! It all will make those that ignore it, a better shot at the moment of truth, rest or not!