I edit pretty much all the tracks in my DJ collection, making breakdowns shorter, or making a DJ-friendly arrangement, or changing some parts here and there, or even adding some bits from other tracks. The way I always have something unique in my sets.
Sometimes I can instantly tell what will work on the dancefloors and what won’t, sometimes I see the crowd’s reaction and only then add a respective note to this track to tweak it later when I back in the studio.
Eventually, all these tracks end up being labelled as “DL Edit”, so I know it’s my edit and not the original version when I play.
Working on a proper music collection is where all the DJ’s hard work is, when you see a DJ is playing is just a tip of the iceberg.