Is the "vin" value field necessary or just a matter of convenience?

Question

I notice that vin has a value field denoting the amount of money being spent from the input transaction. Am I correct that this is here for convenience and must equal the value of the specified transaction output?

The only other case I can think of is splitting the same transaction output into two transaction inputs, but I don't see the point of this.

"vin": [{
  "txid":"672aeb1bc62b3941f2e9a530ff6d12e5e70c257632d536d5b0633e12b68a915d",
  "vout":1,
  "scriptSig":{
    "asm":"..."
  },
  "addr":"1HKqcNrf3NPuz4s2MdoAzpYYfjYvbbsxZf",
  "value":0.0468234
},
...]

Answer 1

That field in the RPC response is by definition just information about the output being spent, so yes, it is always going to be equal.

As for whether it's necessary - no, of course not. But the RPC in the first place exists because of convenience.