It's absolutely a valid question to ask since it seems very much over the top to play 8 finger tapping.
The first thing that comes to mind that makes this a valid technique is the sound that is not really possible to get without using this technique.

If you have been using basic tapping before you will also see that the technique makes you able to play stuff you would not have done with other techniques. Some people will say that its possible to do the job just with legato but its a ridiculous thing to say because why would you make it harder on your self plus the technique in itself just inspires you in another way than
other techniques, so like all the other techniques it has a specific sound and inspires in its own way for you to play in a specific way

The concept of 8 finger tapping also gives you the possibility of adding more
notes to the phrases you play and lets not forget it also looks cool