When working in a multibody part you sometimes have overlapping regions and you need to remove the common volume from one of the bodies. In this example I inserted a derived part as a separate body. Notice the interfering areas where we want a groove in the red body.
We could use the Combine feature with the Subtract option to remove the material from the red body. But this would also remove the black body at the same time.
The other option could be to make a copy of the black body using Move/Copy Bodies, then use one of these for the Combine feature. But this is just another step/feature to add.
Instead you can use the SOLIDWORKS Indent Feature (Insert > Features > Indent) with the Cut option. Set the Clearance to 0 (unless you actually want clearance) and it will remove the region from the ‘Target Body’. Yet it will still leave both bodies at the end with only one feature.