why slide master are important

 The advantages of having slide master is... 

you don't have to go through all the slide and change the background  over and over again. You have to do it once and it does it for all slides, even when you add one.

Another one is that if you want one different you can change it back to normal and it will do it for that one slide.

Also is that you don't have to go thorough and change all the fonts and colours  in text.