If you format your non-google search carefully, you will have found two posts I wrote previously, starting with
https://www.trailmanorowners.com/for...ad.php?t=20204.
A PWM controller "wastes power" by leaving a portion of panel-provided power within the panels (by disconnecting and then reconnecting the panels thousands of times per second). The average (lower) voltage provided to the batteries is reduced to the Voltage which the batteries need to have, for that State-Of-Charge. They can be built small, simple, and reliable at costs around $15-40 delivered. If you need "14.2 volts" into your batteries, but your panel voltage is even higher than 17.9 Volts, you lose a higher share.
An MPPT controller never disconnects the panels while feeding a hungry pair of batteries. Instead, they convert the power being obtained from the panels (at a voltage which is too high), into more current, at lower battery charging voltage. This is a complex process, involving expensive electronics within a much larger box. The bigger box provides a heat sink for a smaller amount of wasted power (5-10%) dissipated as heat while the controller runs in MPPT mode.
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With only a single "100w panel", it would be a poor investment to spend $130-$150 on a decent MPPT Solar controller - gaining only about 15 watts from that panel. It would be far better to add a second solar panel, gaining more "final watts for possibly less money.
The cross-over occurs at about 300 watts of panel power. At that point, adding a 4th panel versus switching to MPPT begins to make the MPPT switch a better deal. For higher power panels (I have about 500 watts, configured at about 80 volts) MPPT definitely wins.