The fundamental difference between TCP and UDP lies in the trade-off between reliability and speed. The general rule of thumb is to use TCP when accuracy is critical and UDP when timeliness matters most.

TCP is used in applications where missing or corrupted data breaks functionality, such as loading web pages (HTTP/HTTPS), sending email, and performing file transfers. In these cases, waiting for retransmissions is preferable to missing data.

UDP is suited for real-time interactions such as live video streams, voice calls, and online games. In live streaming, a delayed packet representing an elapsed moment is useless, making it better to drop the lost packet and continue rather than pausing the stream to wait for retransmission. Streaming systems often combine UDP delivery with techniques like adaptive bitrate to adjust quality dynamically based on available bandwidth.