basic excel training - Macro workbook

When we created a macro yesterday we used it two ways. One we created a shortcut key in the "This workbook" and then we next attached it to a personal toolbar and used it from a button with the macro assigned to it Another option when using the shortcut key was "Personal Workbook" - I often need the same macro in different workbooks so would it be better to store my macros in a personal workbook - how does this then work?