I found a friend in my shoe today.

My rule of thumb: I leave spiders alone, especially if they're tiny and/or jumping spiders.

BUT.

If a spider's body gets bigger than my finger nail, it dies.
If it's especially white or black, it dies. Inb4 racist to spiders.
If it's in my bathtub, it dies.

I may be merciful sometimes, and put it into a cup so I can move it to the back of my yard where it can grow up in peace.