Say Y here is you want IrLAP to send fast RR (Receive Ready) frames
when acting as a primary station.
Disabling this option will make latency over IrDA very bad. Enabling
this option will make the IrDA stack send more packet than strictly
necessary, thus reduce your battery life (but not that much).

Fast RR will make IrLAP send out a RR frame immediately when
receiving a frame if its own transmit queue is currently empty. This
will give a lot of speed improvement when receiving much data since
the secondary station will not have to wait the max. turn around
time (usually 500ms) before it is allowed to transmit the next time.
If the transmit queue of the secondary is also empty, the primary will
start backing-off before sending another RR frame, waiting longer
each time until the back-off reaches the max. turn around time.
This back-off increase in controlled via
/proc/sys/net/irda/fast_poll_increase

If unsure, say Y.