there are some "isolates". I think you mean this:
isolate removes the the history of geometrical element. you will see a "red sign" in the feature tree. "isolate" is similar to "create datum mode".
isolate command is used to extract a profile from a 3-d object........ for eg. u have a cylinder select its plane such that u see the circle ,,, now if u wanna sketch another circle wid same diametre u can do it in 2 ways one is dat u go to sketch select circle to draw a circle and then make it coincident & concentric by constraints tool or by using isolate command <<< u select sketch of circle from top view of the cylinder>>> <<< then right click on the yellow unresolved sketch>>> <<< select mark object then isolate>>..