Lets say you are running low budget campaign and new ad starts to perform really well. You want to increase budget to take use of it but if you do it without thinking then you will jsut waste your money.
I had Facebook campaign and it was running 2EUR a day. Ad for my latest post related to end of world started to perform really well having CPM of 0.01EUR and it generated a lot of likes, comments and shares. Now I wanted to take use of it and increased budget 5 times from 2EUR to 10EUR. What happened is that after 15 minutes all of the 10EUR was spent, CPM went up from 0.01 to 0.11 and there was only a little extra action.
Please bear in mind that if you do changes to you successful campaign then to this bit by bit. Facebook and google advertisments engine will overcompensate and all of your money will be wasted.