It's not as black and white as you suggest. Perhaps one believes that the current bet is still a good one but prefers to alter the trade's parameters after price movement. Options offer you the ability to tailor the risk/reward to your liking and adjustments (rolls) achieve that.
A simple example. XYZ is $100 and I buy a high delta 6 month $80 call for $25. XYZ quickly rises to $115 and I roll the $80 call up to a strike of $95 (same expiration) for a credit of $13.
At the cost of some delta, I've lowered my cost basis and I have practically the identical position (bet) as I originally had except at a higher underlying price.
Another example. Suppose I'm selling naked puts to acquire a stock at a lower price (or keep the income if I'm not assigned). If XYZ is has not changed much as expiration nears, the premium will have dwindled.
So it's a week until expiration and I still would like to own the stock. The short put's premium is 5 cents. The 3 week same strike put is 45 cents. Why should I wait one week for 5 cents when I can collect 40 cents for 3 weeks after the roll? That's 13+ cents per week. It's a no brainer. Roll the put.