ProsEasy to learn and use – Most machines have a picture demonstrating its use, which for most machines is pretty self explanatory. This makes them easy to use on their own or with other machines to create your own circuit. If hiring a personal trainer is out of your budget, they are easy to figure out by simply watching the person ahead of you.Isolate muscle groups more efficiently – Since most of your body is pretty stable on most machines you are able to target the larger muscle groups more efficiently. This is beneficial to those who have a solid foundation and are looking to improve their physique by building bigger muscles. This can be the preferred method for some bodybuilder types.Allow you to train with heavier weights without assistance – If you are fairly inexperienced with proper technique when using free weights, it may be difficult to add resistance. Some machines will allow you to slap on extra weight without risk of injury. This may also be useful if you are pressing or squatting without a partner or spotter. (Note: proper technique is paramount before you need to worry about adding weight. Train smart.)May be useful for elderly populations and/or rehab – For someone that has a really low level of fitness and/or is recovering from an injury, machines may be the tool to get their strength up quickly and safely. Since machines isolate it may also be easier to work around certain injuries.ConsNon-functional – Although machines will make you bigger and stronger, they don’t train complete human movement patterns (See: primal movement patterns) that are necessary to, well, move. Perhaps the worst machine is the Smith Machine which locks you into place for heavy exercises like squats and bench and doesn’t take into account different body types, which is a recipe for disaster. Weight machines just don’t translate well into strength and fitness for daily activities, not to mention athletics.Neglect smaller stabilizing muscles – Since you are isolating target muscle groups, the important stabilizing muscle groups around the joints take a back seat. If you neglect these smaller muscles for too long, you run the risk of chronic injury and poor posture.May cause injury directly and indirectly – Although safer to use with lower levels of skill, it is still possible to use too much weight and enough poor form to cause a serious injury. Overloading the same movement day in and day out is also an easy way to set yourself up for an overuse injury. Form is important and like anything else the danger is in the dose!Fill up during peak hours – If you have ever worked out in a commercial gym during peak hours you may have noticed that every machine in the place seems to be filled up. Instead of waiting for that guy that has been on the machine bench press for 20 minutes to get up, head over to the free weight area for some more breathing room.