The reason for being able to alter widths is so the tractor can be altered to fit up different row widths, or to suit ploughing. A side effect obviously is that the wider they are the greater the stability. Another side effect is that the wider you do the hevier the steering becomes... dont ask me why, its just an observation from experience. The 'normal' widest width comonly used is 60" as this was correct for potatoe rows. I wouldnt go any wider than that for everyday use. Better if you have a real stability issue to take up previous suggestion of double wheels. Easy to to because special adaptor bolts can still be purchase new, an extra set of wheels can then just be bolted on when required. It all obviously costs money.
Changing wheel track widths is damned hard work , ive done it quite a few times as i have my favorite tractor set for potatoe rows, but then sometimes (once a year) take it to a ploughing match. Most farmers in the seventies and eightys moved to 2 tractors one set at each width, but my dad used to recall altering wheel widths a couple of times a day to suit operations in his early days on the farm when they only had one........but then they made him milk on his wedding day !