I think there are three typical uses:

1. Building consensus on the block chain. This is what the core is for.
2. Single user wallets. This is where SPV alone is good.
3. Services e.g. exchange, payment processor .... This is where core + indexing server talking SPV to core is the right choice

Regards,

Tamás Blummer
Founder, CEO

http://bitsofproof.com