Why does binding your values with placeholders actually create additional DB IO for your query?

It doesn't, always, but it can. It depends on the query plan generated with vs. without parameters. I assume your real query is not as simple as you have above, otherwise there would probably be no difference in query plans. Maybe you (or the DBAs) just need to update statistics on the table, but maybe, without knowing what specific values you're going to bind, Oracle can't figure out what the most efficient (or even what a decently efficient) query plan should be. This can happen on queries that include things such as LIKE clauses, e.g. 'LIKE ?' where Oracle doesn't know if you're going to bind 'ABCD%' (which can use an index) or '%ABCD%' (which can not).