I only use shapeshift if I know I need an altcoin fast. It rarely comes up, but it's handy when it does. The fees are high so it's not something I would do regularly (like if you're planning on day trading altcoins) but if you want to trade 100 obscure altcoins for 75 of some other obscure altcoin it is the place to go. The other choice would be to go to a large exchange, place a bid to sell your coins for bitcoins, then trade those bitcoins for the other altcoin you needed. You're mainly just paying a convenience fee.