Send the message unreliably. Can be lost. Messages can be larger than a single MTU (UDP packet), but there is no retransmission, so if any piece of the message is lost, the entire message will be dropped.
The sending API does have some knowledge of the underlying connection, so if there is no NAT-traversal accomplished or there is a recognized adjustment happening on the connection, the packet will be batched until the connection is open again.
Disable Nagle's algorithm. By default, Nagle's algorithm is applied to all outbound messages. This means that the message will NOT be sent immediately, in case further messages are sent soon after you send this, which can be grouped together. Any time there is enough buffered data to fill a packet, the packets will be pushed out immediately, but partially-full packets not be sent until the Nagle timer expires.
If the message cannot be sent very soon (because the connection is still doing some initial handshaking, route negotiations, etc), then just drop it. This is only applicable for unreliable messages. Using this flag on reliable messages is invalid.