Many people shun training in higher rep ranges because they feel it's "too light" to build muscle and make progress. I'm here to tell you that there is value in almost every repetition range for nearly any athlete, whether they want to build muscle or focus on gaining strength. A well rounded training program that utilizes repetition diversity is a great well to cover all of your bases and get the most out of your training.
Builds Muscle & Endurance
Some are of the mindset that in order to build muscle, you need to lift heavy. Truth is, most rep ranges (6-30) build the same amount of muscle when proximity to failure is controlled for. By choosing a light rep range, you don't miss out on hypertrophy and can rest assured that your training sets are building muscle mass, provided you are taking them close enough to failure.
Lighter rep ranges are also superior for building muscular endurance. By utilizing higher repetition work, you'll increase your ability to perform work for longer periods of time. A pretty solid attribute to train for everyday life and overall fitness levels.
Lighter Loads Produce Less Fatigue
Lighter rep ranges produce less overall training fatigue. Because of this, lighter rep ranges are great for maximizing how much volume you can perform per week. This means that even if your goal is mostly strength, higher rep work can be a valuable tool to use for your accessory and isolation movements, which are mostly programmed to build muscle in the areas that will assist your strength on the main lifts.
"Lighter" training days that utilize a lot of high rep work can be a great tool to enhance your recovery without losing out on hypertrophy. It's not uncommon at all (for good reason!) that many programs have heavy days and light days. It's a very good strategy that's tried and true to help you continue training for long periods without driving yourself into a recovery rut. There's no reason to always train in just one single rep zone. You miss out on nothing by varying your rep ranges.
Lighter Loads Are Less Intimidating
Many trainees become intimidated by heavy loads, which can sometimes negatively impact their performance during a set due to inhibitions holding them back from pushing as hard as they could. This is far less common with lighter loads. Since lighter loads are much less intimidating, most go into them with confidence and are thus more likely to perform at their peak. This may lead to a more consistent pattern of performance during lighter rep training.
Utilizing these lighter rep ranges may be a good strategy for new lifters who are intimidated by resistance training by starting them with lighter loads and slowly introducing them to heavier loads as they get more comfortable under the bar.
Can Shift Muscle Focus
Some exercises may target different muscles depending on the rep range used. This varies from exercise to exercise and even between individuals. One common example is the bench press. Many trainees report that higher rep bench press work tends to favor the triceps more than the chest and vice versa.
Because of this, it's important to train in a variety of rep ranges with different exercises so you can get a better understanding of how you'll respond. This can be a great tool to fully develop your muscles, rather than always hitting them with the same relative loads and angles.
Easier Mind Muscle Connection
Often times when a trainee lifts heavy, they have a hard time really focusing on the targeted muscle. Very heavy loads can lead to more "cheating" or use of momentum to finish a set when they become difficult. When doing a very heavy set, your mind is often less focused on contracting the actual muscle you want to target and is more focused on simply getting the weight up each repetition. With lighter training, not only do you have less need for momentum, but you also have more repetitions to practice contracting the muscle you're trying to target and ensure that you're not using too many other surrounding muscles to get the weight up.
I do want to clarify that the "mind muscle connection" is not some secret trick that is going to get you jacked once you learn it, but understanding how to properly contract certain muscles during certain movements, especially compound movements, is important. A common problem, for example, for newer trainees is a difficulty in actually getting their lats to contract during back movements, which shifts the emphasis onto other surrounding muscles. Performing only heavy back movements can leave them without a chance to practice getting their lats to contract. By doing lighter work, they can really practice pulling with their lats instead of other muscle groups.