Using heavy weight

Question:
If my goal was to build muscle, and to also lose fat, should I stick with heavier weight/low repetitions for the majority of the time?

Answer:
It's a really good idea to introduce different styles of training, because in the end, the body responds best to change. On this site you'll see a lot of information about the basics to building an effective muscle building/ fat burning workout routine, but even these basics can be slightly adjusted.

You can cycle different routines, or approaches to those routines, by adding different exercises, increasing or decreasing your rep ranges, or adding intensity methods to your workout to throw the body off guard. If the body adapts to a workout routine, it'll eventually plateau. Meaning, keep it changing, and add variety.

Muscle building results will happen a lot easier and faster when using a lower rep range. Short intense muscle contractions is the proven way to build muscle faster.

Yes. The majority of your workouts should be in the lower rep ranges, while periodically introducing slight changes, such as higher reps, then going right back.

There's so much experimentation that goes on here. It's recommended to try several approaches.

The idea to build muscle is to deliver as much stress on the muscle as possible; there's several ways to do this.

Some people may do 20 reps.... Will that destroy your muscle> No! Should you do that many reps all the time? No! Why? Because that would mean you aren't using much weight. This wouldn't stress the muscle into much growth at all.

If you are a person who is wanting muscle gains, stick to lower reps. 8, or 10, 12...

There's really no magic number. Your rep ranges are going to change all the time, because if you're doing it correctly, you will be introducing new routines all the time!