High Reps and Light Weight? Or Heavy Weight to Failure?
What will get the best results with weight training...heavy weights and lower reps, or lighter weight with higher reps? I say BOTH. BUT, you have to start somewhere if you are a beginner in the gym. Beginners should definitely start with lighter weight and high reps to build up muscular endurance and not get injured trying to force using heavy weights. You have to work your way up to the heavy ones. Progressive Overload is how you train your muscles to get stronger and stronger over time...progressively using slightly heavier weights each month.
Higher rep ranges are 15 and up, typically 15-20/25. Quicker rest times between sets. Heavy rep ranges are 1-8/10. Longer rest time between sets for recovery for the next set. Powerlifting/Strong Man dudes train in the heavy 1-5 rep range. Getting our muscles to failure is where the most muscle damage happens, which in turn "muscle growth". So whether we get to "failure" at 25 reps, or in 5 reps, we are still doing enough "damage" to our muscles for growth. So whichever rep range you choose to train in, just make sure it is really tough to get to that last rep, if you are counting. Fail at that 5th rep, or fail at that 12th or 25th rep, whatever it is, it just needs to be challenging enough to breakdown the muscle in the gym, so at night when you rest it can grow.
Once you have graduated to intermediate in the gym and feel comfortable to start grabbing the heavier weights, go for it! Trade off some weeks of higher reps 15-20 and 3-4 sets, then switch it up to heavier weights at 5-10 reps and do 4-5 sets. DO EVERYTHING. JUST MAKE SURE ITS CHALLENGING ENOUGH FOR CHANGES TO BE ABLE TO HAPPEN.