When you use the Add Edit function it places a cut in a track wherever the Position Indicator is parked and, by default, it's programmed to place the cut onto any track that has its Track Selector enabled. However, if you hold the option/Alt key when you use Add Edit, it will do the following:
In Source/Record Mode, it places the cut(s) only in Filler. In other words, it will not cut segments of video or audio. Additionally, it will place cuts on a Filler track even if its track selector is not enabled.
In Trim Mode, it will do everything it does when used in Source/Record Mode but, the great part is that in Trim Mode, all the cuts you make will also automatically become enabled for Trimming. Because the option/Alt + Add Edit function only relates to Filler, there may be instances where you'll have to then manually configure the Trim Rollers on the tracks containing video or audio segments. So be sure to read these related...