Can Time Machine restore erased drive?

[Gazudara]

Hello!

Regarding my previous thread, I got sudden question:

If I erase my current drive, can I simply hook external hard drive to my Mac and push restore?
Or do I have to first install clean OS from somewhere else and only then can use Time Machine back-up?

I've tried to search for answer, but the few threads I've found don't give answer to this exact question.

According to this, one has to erase Sierra completely, but I have no way to clean install El Capitan from scratch. Only thing I have is Time Machine back-up.
http://www.macworld.co.uk/how-to/ma...ierra-el-capitan-remove-macos-sierra-3581872/

 

[KALLT]

You can restore it completely. Time Machine also has its own recovery environment that you can boot into.

 

[gnasher729]

If you erased the drive, you can just restore from Time Machine. MacOS hides the software for restoring Time Machine somewhere on your drive, and it usually doesn't get erased.

If you _completely_ erased the drive, or if you purchased a brand new drive, then when you try to boot your computer, it will tell you that it needs to download some software first (disk utility, time machine and some others), you'll have to give it an internet connection so you better know the password for your router, then it downloads, and then you are at step 1 where you can restore from Time machine.

 

[Gazudara]

You can restore it completely. Time Machine also has its own recovery environment that you can boot into.

One additional question - if I make Time Machine back-up now and use that after wiping my drive, could current slowness-issues carry over?

EDIT: how many times should I erase the disk?
And would it be dangerous to leave things as they are (downgrading from Sierra without first erasing disk)? I only notice very small slowing down after downgrading without erasing disk.