There is a very slight different in the two methods of baseline metabolic calculation. My trainer used some method last year to calculate mine and came up with baseline of 1240 cals per day. So I do a custom here at Fitday and use her number for me.
Showmenow is correct. Your baseline is what your body uses just to stay alive with your normal, regular level of activity. So even if you work out hard at a gym in the evenings, or walk every afternoon, if you are sitting down at a desk all day (like me unfortunately - how did I end up here???), your baseline is lower than someone who is waiting on tables for example.
From what I read online, the differences between the two methods of calculation are insignificant for the general population. Only matters for hospitalized patients in nutrition calculation.