How important is getting the water to the right temperature before steeping tea leaves?

Just what's in the title.

I drink black, white, green, and whatever teas I can try from various international stores. I know that they are to be steeped at different temperatures but my tea kettle just has one temp so that's what I have been using for years and years.

I wanted to ask the community how important the right temp is for various color teas.