It ties your one address (the one receiving these BTC) to some of your other addresses. This happens when your wallet bundles amounts from your various addresses into one total amount you happen to send.  Transactions with many inputs to form a larger output give whoever wants to look assurance that the same person owns all the input keys.

Like dust sprinkled to make a light beam easier to see, this is just dust sprinkled randomly to make block-chain key ownership analysis easier.