What Is That Purple Line On Your Brush Tool In CC2018?

A big question I've been asked is what that purple line is on the brush tool after they upgraded to Photoshop CC 2018. I want to tell them it's like Clippy for Photoshop (if anyone remembers that from Microsoft Word). 

I want to show you what it is, what it's used for, how to turn it off, or hide it!

In sum: Once the brush is active, go up to "smoothing" and bring it back down to 0% to regain the "original" brush tool. 

Or, you can go under Preferences and Tools and simply hide the "brush leash" when drawing. 

It's used to smooth out brush strokes, but unfortunately it stays on by default!

Credit:
Photo by Bella Kotak www.bellakotak.com