I would assume the the "+ 0" tells Oracle to do a full table scan. There are people who believe that a full table scan is always cheaper than an index lookup. So someone might force the full table scan. It would be the same thing if someone were to do an upper() or lower() or to_char() on the left side of an equation. If you have something other than just a column name on the left side Oracle might decide that a full table scan is the only way to go. The exception is that if you had a newer version of Oracle and a function based index.

It should be safe to remove the "+ 0", but test anyway.