Life is busy and you need to make a sacrifice both in time and money to go to a gym 2 to 3 times per week to exercise, so it’s best to use your limited time to get as much benefit as you can. The whole point of any exercise routine is to get your body to function and perform better, whether it be in sporting activities, or in the mundane of everyday life. Machine training is great for getting ‘show’ muscles like bigger biceps for a summer tank top, or poolside on a vacation, but for the functionality of everyday life, such as lifting luggage, moving furniture, carrying a TV from Fry’s to the car, or balancing on a ladder to reach up to a shelf, these isolated now bigger muscles are useless. What use is there to bigger muscles without it translating to being able to go about the routine of daily life more ease. .
Machines quite simply due to their isolation of individual muscle groups, are not effective in creating the duality of translating what you can lift, verses what is demanded of your body in the ‘real’ world. I’m sure it will start to make sense to you by now, that sitting and just moving your arms, or legs slowly up or down will do nothing to improve your everyday mobility or performance.