Creating a rough texture that will look realistic is not always easy to do. You can do it using a simple pencil or with a painting software that will do the work for you.
But doing this using a software can be tricky. Beginners will be tempted to overload their creations with cool effects (and that is perfectly normal) turning what could have been a piece of artwork into a digital mess.
It's important to handle any effect with care and judgment. A good effect is one that people won't notice.
If your readers are constantly looking and admiring the textures you have created, then they will miss the whole point. Let's take one example and see how one simple effect can be applied differently.
In the first example, this texture was created by a beginner. Someone who is working with a painting software for the first time and want to impress all of his friends.
The result is not enjoyable! The textures are too obvious and there are too many of them! In the second example, the texture is, on the opposite, too subtle. It's useless to add a texture if the user can't see it. Unless you mix this texture with other textures or some other effects like shadows.
In the third example, the artist chose the wrong textures. They don't really fit with the subject and are highly irrelevant.
You probably wouldn't choose a picture of a piece of wood to create a wall of bricks. It's the same thing with textures. Use them wisely.
The fourth example is more accurate. The textures are relevant. They are not too obvious but still visible.
And, most important, they do add something interesting to the drawing. They add another dimension that would not be possible to do with a simple pencil!