LLC retransmission occurs at the LLC layer and not at the RLC layer.
Have you ever wondered why there is an requirement of another logical link, i.e. LLC, above RLC, between the MS and SGSN?
There could scenario where LLC retransmissions will be required, for example, for an application that works in an unacknowledged mode and which do not have an error checking and correction mechanism on it own.
Due to LLC retransmission, timer running at TCP layer may expire. This will make the TCP to re-send the Network PDU (NPDU), for whom an ack was awaiting, to the LLC layer , which could further add to a delay in the TBF establishment or even a dip in throughput.