When you use a trigger (hot key, device key, or typed string trigger) that is assigned to more than one macro, and all of these macros are active, then Keyboard Maestro does not know which macro to trigger.
So instead, it displays the Conflict Palette listing all the triggered macros and lets you select the desired macro, either by clicking on it or by typing a letter that narrows that palette down until only one macro remains at which point that macro is triggered.
You can use the Conflict Palette to limit the number of hot keys you need to remember by giving a bunch of similar or related macros the same hot key and then selecting the desired macro with a further keystroke based on the now visible palette.
You can control the appearance of the Conflict Palette in the Palette Preferences.
If you are having trouble understanding Macro and Macro Group Activation, or trouble controlling when Conflict Palettes appear, then take a look at these Keyboard Maestro Forum posts.