What year is your Mustang?
I had a 2" drop with my Eibach Sportlline springs. Your probably going to scrape on the inside of the front fender (that plastic wheel-well) I had to shave some of it down so I didn't scrape.
Aside from that, I have no problem getting around town. Sometimes my exhaust scrapes, but very rarely. CC plates and a good stiff set of shocks will help a LOT.
You can get by without them for a while, but not for long... the inside of your front tires will dissipate and your stock shocks will go bad pretty quick.
Also, DONT forget to transfer the stock rubber peices from your stock springs (I cant recall what they're called) If you leave them off, your car will drop more than 2".