What is the purpose of adding an inductor to a Pi-network to create a Pi-L-network?
Why A Pi-network is already a low-pass filter, but adding a series inductor (plus the load capacitance) tacks an extra L-section onto the output, so the signal passes through two cascaded low-pass sections instead of one. Each additional reactive section increases the rolloff slope above the cutoff frequency, so harmonics of the transmit frequency are attenuated much more strongly. That is why classic tube transmitter tank circuits used the Pi-L configuration for final amplifier output.
Watch out Greater transformation range sounds plausible because the extra section does help step down to low impedances in stages, but the recognized purpose in the pool is the added attenuation of harmonics. Efficiency actually drops slightly, since every added component has some loss.
Pi-L = Pi plus one more L-section = one more low-pass stage = cleaner harmonics.