When a programmer decides to use UDP as a transport protocol, what is a decision factor?

When a programmer decides to use UDP, it is normally because the programmer is sequencing and acknowledging datagrams already. The redundancy of acknowledgments at the Transport layer is not needed. Guaranteed delivery of segments is not a function of UDP. UDP does not provide windowing flow control because acknowledgment is not a function of UDP. A virtual circuit can only be created with a setup and teardown of communications, such as TCP offers.