I think you should be able to start where you left off at. You use boosters to get passed a level and you start over then you don't have the boosters if you get to that level again.
I use the boosters on levels that I think I need themon and find out that you need them for another level. I don't have extra boosters or coins I do what I can with what I get or have. It's hard.
Well I made it this far so far but haven't got to level 4 yet since this morning. Hopefully I get passed this and move on so I don't have to start over. That sucks to start over.