Odds are you will not simply be towing a banner for 1250 hours. You will be exposed to business and economic pressures that you never experienced in training. Your boss will make comments about maintenance costs, fuel, and revenue. That pressure may affect your decisions as a pilot in an insidious way.

The tire might look a little worn, but you just caught this after the last mechanic left for the night right before a flight. Are you going to cancel the flight or are you going to go? Maybe you decide to go and get lucky and make it back, maybe you don't. Either way, you are likely going to remember that uncomfortable feeling you had as you realized your actions can have a huge impact on revenue. Maybe you decide to change your work habits and get to the aircraft early to preflight the thing before the mechanic leaves.

How would that translate into the 121 world? The weather may be bad on the day you plan to commute into work. Those 1250 hours you worked as a professional pilot taught you the value of being conservative and acting proactively, so you decide to commute in the night before.

And as far as bd habits are concerned. Seeing how 90% of the pilots in the US had a more than 1,000 hours before they got hired at an airline whatever bad habits they had are things the training department has seen before. I would argue that over the 2 years it takes to build 1,500 hours you would likely figure out what habits are bad and what are good.