WA/WB Strategy?

[Gorgias]

I have a general question. A lot of hand histories talk about wa/wb. I know that this means "way ahead/way behind", but what does it mean in terms of strategy? Ie, why should I (apparently?) be so conservative when it's a WA/WB situation?

If there's a stickied post on this, please just send me there... I looked around but couldn't find anything on it...maybe I am just blind.

Thanks everyone