Essentially there are two types of strength: one-rep strength (muscular strength), and muscular endurance. If your max squat is 350lbs, and mine is only 300lbs, then you have more muscular strength than me. On the flip side, if I can lift 250lbs 10 times, but you can only lift it 8 times, then I have more muscular endurance than you. Some people specifically train for maximum strength, such as powerlifters, while other people may train for muscular endurance. Many believe, including me, that bodybuilders need both to be well-balanced. If all you ever train for is muscular endurance, lifting a lower weight in a higher rep range (10-12, 10-12, ect..) then you will still be able to cause muscle overload and induce hypertrophy to grow, considering your diet is appropriate, but you may tend to look soft. Heavy weight and power sets build muscle density, which is why many bodybuilders will incorporate the best of all worlds into their training; starting a set of a particular exercise in a higher rep range, and progressively increasing the weight, decreasing the amount of reps they're able to perform, thus increasing power. Heavy weight and power sets build muscle density, however, in bodybuilding, muscle endurance is equally as important as sheer strength, for numerous reasons. So combing the best of all worlds is one of the better routes to go, in mine and other's opinions.
Back to your first question... If you mainly train using all power sets, staying in the lower rep ranges, then you'll tend to be more powerful and able to lift more weight. But if you lower the weight you may not be able to lift it X number of times compared to the next guy who may not be as "strong" as you, who trains for muscular endurance. So combing different principles in your training, training for both power and endurance, in the long run is a good bet to take. You'll be able to build muscle density, and be able to throw up a lot of weight, but you'll also have more muscle endurance. And remember, in bodybuilding, weight is the means to an end (as opposed to another sport such as weight lifting and powerlifting), but there are advantages to using power sets in bodybuilding (increasing muscle density).
As far as your second question goes... If you change the angle of movement on any exercise, you're going to tend to recruit different muscles, or different areas of the muscle, to aid in the lift. Now sometimes you explicitly do this, such as flat bench compared to incline and decline bench, or variations of biceps curls, and so on and so forth. However, sometimes when you change the angle of movement, you could be doing more harm than good. I'm not saying you were doing anything wrong, I'm just saying that when you alter the position of your body relevant to the weight your lifting, relevant to gravity, your body will adapt accordingly, be it for the better or not. Just be careful when you try something new, and always listen to what your body is telling you!
Hope that helped some.. Good luck with your training bro!
