BTC as reserve currency and for major purchases: house, car, property, million dollar international payments. LTC for buying coffee.
I used BTC to buy a $5 steam game. It worked just as well as major purchases. Why would I want/need a second currency just to handle smaller purchases?
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LTC/Scrypt is also a hedge against BTC/SHA256 and as such helps to secure the entire cryptocurrency economy.
There is some truth to this however a partial break of SHA256 doesn't materially affect mining. If people can mine 100x more efficiently then difficulty will simply rise 100x. On the other hand a complete break of SHA256 (such that collisions can be found trivially easy) presents a danger to the security of addresses and LTC has chosen to use the same address structure as Bitcoin making it equally vulnerable. The good news is the likelihood of that is very low, and the likelihood of it happening quickly before changes can be made is even less likely.Of all of the cryptographic primitives used in any cryptocurrency it is the public key cryptography which history has shown is the most vulnerable. It is vulnerable not just to future Quantum Cryptography but also to improved cryptoanalysis. Take RSA for example. It is now possible to break 768 bit RSA keys making 1024 bit keys vulnerable to attack within the next decade. Most systems using RSA have moved to 2048 or 3764 bit keys to provide improved resistance to advancement in cryptoanalysis.
A future alt coin which uses a different public key cryptographic system would provide a better hedge/insurance then one which uses a different mining algorithm.
i see what you did there 
