Flush on full means the data is only sent when the buffer is full. If the buffer is large and you have an optimized game that minimizes the amount of data sent

Flush on full means the data is only sent when the buffer is full. If the buffer is large and you have an optimized game that minimizes the amount of data sent then the buffer takes longer to fill up and packets are sent less often. Older games that send more data may get quicker response if your throughput is high but your packets are large