Isolation exercises means doing exercise of the bigger muscle groups at different angles and at low intensity for so called muscle shaping.
Everyone knows that basic exercises are limited like bench press, front press , squats , dead lift , chin ups , barbell curls etc. Where as isolation exercises are many for all the muscles like precede , cross pulley, inclined & declined bench presses, dumbbell presses & flies etc for chest , lats pulley , ground pulley & rowing etc for lats , preacher curls & concentration curls etc for biceps , leg extensions & leg curling for legs etc. All these minor and assistant exercise are normally done with 40 to 60% load of the one repetitive power. Thus they are sort of low intensity exercises for shape up, toning up and cardio benefits.
These exercises don't improve muscles size, mass and shape. Yes, they work as cardio to lower your Body fat, thus showing some improved definitions.
The only exercises which can give you size , mass , strength and ruggedness are the high intensity basic exercises not the light isolation exercises which could be injurious and laborious involving some part of the muscle not the whole muscle or muscle group.