Sag on all bikes is important if you want your suspension to work at its best and the bike to steer and turn at its best as well. It's what tells you if the bike has the correct spring rate for your weight. If after setting the sag to 1/3 of travel the bike itself unloaded sags beyond 15mm from fully up, the spring is too light or it sags less than 15mm it's too hard. That's long travel dirt bikes at 15mm, less travel roadys is a smaller dimension. Sure you can potter around on any bike set-up or not, especially if you are in the typical design range of 75 to 90kg body weight but if you ever try a bike set-up right to your weight it's amazing how different it is. Too much sag and the bike will steer slower, and take more effort to change line. Too little and it will steer quicker, maybe even be unstable, especially on bumpy corners. It's a pain in the arse but doing this is a 2 person job unless you have 2 mitre long arms. In my case with the Atlas, it sags 16mm too much in the rear now, BTW spring preload will do nothing to fix incorrect spring strength and that's effect on ride quality, in the long run, it WILL need at least a stronger spring. To early to tell if a shock will be needed as well. Here is a quick example, pre-Terry Hays setting up my modern Husky it was horrible in high-speed deep sand woops, you had to work hard not to crash poping the front up just before hitting each woop or it would try and kill you after Terry Hays you could pin it and shut your eyes. Light years better.