Hi Davison
1. There are Two Work centers in IW38 screen, See this picture:
2.Both Tcodes take you to the same Program screen (SAPLCRA0). , the Value of WorkCenter Cat differ 0005 for Maint. Work Center. and 0001 for the Other (Prodn Work Center, Often PM people do not use this field).
Hope your doubt is cleared.
Jogeswara Rao K