#1
How important is it to cover all the registers when making a piece of music?

Does it vary depending on the type of music that you're making?

To be honest I'm not even sure how many registers there are in modern music. When I say register I'm referring to for example C1>C2>C3>C4>C5>C6>C7>C8

Also as a side question, how many registers are there exactly?
#2
Not important at all. It's totally down to the type of texture you want to hear.
.
#3
Registration is definitely something you should pay attention to, but there's no rules as to whether it's good or bad to work within a small register or to have more sprawling registration. Like Nietsche said, it's about what kind of texture(s) you're looking to create.
#4
I see. So although Registration isn't something that has rules It is definitely an important tool when it comes to creating different textures.

For example lets say I wanted to create an thick, in your face texture.

In this case I would assume that having all the registers covered would be very important.

However if I wanted the texture to be thin then I may only incorporate a few registers as opposed to all of them.

Is this the right idea?
#5
Texture about is more than just register. You could create a dense texture by just using the middle register alone for example. It depends on what timbres you're using, the instrumentation, and the type of voicing you're using if you are writing that kind of music. Again, you could change that texture into a thin one by changing what registers it is being played in. Experiment and you'll figure things out.
#6
It depends on the instruments used. Most of the time in a rock band bass plays in the low register and guitar plays in the middle register. And when there's a guitar solo, guitar usually plays in a higher register.

But you don't want to use as many registers as possible in a song for the sake of using them. Just use what feels good.
Quote by AlanHB
Just remember that there are no boring scales, just boring players.

Gear

Bach Stradivarius 37G
Charvel So Cal
Fender Dimension Bass
Hartke HyDrive 210c
Ibanez BL70
Laney VC30
Tokai TB48
Yamaha FG720S-12
Yamaha P115