When All Targets is selected, you can set the compiler options that you want to use when compiling an application targeted for all of the target platforms.

[? ] will appear in a check box if an option is checked for one target and unchecked for a different target platform.

[ ] If All Targets is not checked, your code will be compiled with the options set for each of the selected target platforms.

Multi-target options are available when using BP or BPW.