Quote from rallymode:
Andy,
if you havent read any of cottle's books i highly recommend you do. You will get a great understanding of how to build positions and how to adjust them and when it makes sense to.
Bottom line is, adjustment is better than a simple offset ONLY in those cases where the new position completely aligns with your opinion of the market or when you get better pricing on a lock with the second leg than you would when you offset(which is hardly ever the case). Often traders have the illusion that because they leg into a position when the market moves in their direction they have a better trade. You really have to make sure you would open the position you are trying to adjust to even if you didnt have the original leg.
Example, you buy a bull call spread. The market moves in your direction and you decide to turn it into a FLY instead of offsetting. You dont think the market will churn but you do it anyway cuz now you have a free fly. This is an example of when not to adjust. Remember, you took directional risk on your original vertical which you didnt get compensated for. To make money now you have to be right twice. you really must not look at the FLY as a free one to make a clear choice whether its good to adjust or not.
I hope that helps.