couple of questions..newbie sa maintenance ng kotse.

what's the worst thing that could happen if i haven't tuned up my car?
about 15k na since the last tuneup. runs great pa rin naman. starts fine. no problems i have noticed. city idsi 2007 ang car.


about sa gas.
who uses the e10 gas?
is it cheap because of the octane level? easier consumed? or what?

mas mabilis ba mauubus ng kotse ang 10 liters ng e10? or 10 liters ng regular unleaded? or parehas lang yon?

disadvantages?

thanks sa answers...