Why do some transactions have multiple inputs from the same address?

[bootmii]

I often see transactions with more than one input with the same address. Why?

[eleuthria]

I often see transactions with more than one input with the same address. Why?

When sending coins, the inputs used are previously received amounts [outputs from other addresses, or possibly even the same address].
The balance of an address is the sum of unspent inputs.  When sending coins, you must reference these unspent inputs to create the outputs.

- Address 1Guy has 10 BTC in total, made up of 10 individual 1 BTC payments from various sources.
- 1Guy wants to send 3 BTC to 1Girl.
- 1Guy's transaction to 1Girl requires 3 separate inputs to complete the transaction.

[SRoulette]

I often see transactions with more than one input with the same address. Why?

Its often a result of gambling on sites like ours or satoshidice as we send payouts back to one of the input addresses.
This can result in one address having large sums of different sized inputs if played long enough on a wallet such as blockchain.info.