The options are sent to the php_mongo_runcommand function:

```
document = php_mongo_runcommand(c->link, &c->read_pref, Z_STRVAL_P(db->name), Z_STRLEN_P(db->name), cmd, options, 0, &connection TSRMLS_CC);
```

Perhaps no options are used *yet*, but that doesn't mean they couldn't be there in the future. It doesn't really harm having this argument though.