Adjusting Calories Daily vs. Eating Same Amount

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I just joined MFP and really like the site and IPOD app...I've used different calorie counters over time and this is by far the best I've found (and free!).

One question I had for discussion was on adjusting calories on daily basis - i.e. focusing on net calories and moving the total calories consumed based on whether I exercised that day.

It makes sense to me but I used to work with a Personal Trainer at 24 Hr Fitness and their method was different. They calculated a daily intake based on your info and how many times a week you were going to work out. I was to eat the same amount every day whether I worked on that particular day or not (the calculation assumed 3 day/week workout). So for me, it calculated 1860 cal/day - I ate this day in and day out. We would only adjust this if I radically changed my workout schedule (i.e. only working out 2 days/week or increasing to 5 days/week)

I'm curious if one would see a major difference between the two methods....
Mike