WriteBufferOpen is an overloaded method used to enable write buffering for the IOHandler. 

WriteBufferOpen allocates the TIdBuffer instance used in the WriteBuffer property that stores values to be written to the IOHandler connection. 

WriteBufferOpen calls an overloaded variant of the method using -1 as the threshhold that indicates the number of bytes to accumulate in the write buffer prior to flushing to the IOHandler connection. The default value is -1, and indicates that all existing data in WriteBuffer should be flushed at the next opportunity. 

Use WriteBufferClose to disable write buffering for the IOHandler. 

Used WriteBufferFlush to force existing data in WriteBuffer to be written to the IOHandler connection.

TIdBuffer 

TIdIOHandler.WriteBuffer 

TIdIOHandler.WriteBufferClose 

TIdIOHandler.WriteBufferFlush