The short answer, "it depends". An MPPT
controller attempts to maximize the output from the solar panels
by tracking the optimum DC voltage from the panels. And the DC voltage is directly tied to how much sun is on the panels.
If all of your panels receive the exact same sun exposure then a single
MPPT controller, with the panels in series or parallel will work fine, be cheapest and simplest, and get you the most power for your $.
But, on boats, it is frequently difficult to get the exact same solar
exposure on all of your panels. One may have a hard shadow from the boom or some piece of rigging
while another is in full sun. These shadows will cause the DC voltage to drop on that panel. An MPPT controller connected to all the panels can only find one solution to the maximum power point, and it will likely not be the optimum solution for all of the panels if some are shaded and others are not.
Hence the "one controller per panel" recommendation, that way each controller can optimize for the conditions on each panel. Is it worth the $/time/effort? Depends on how much different the solar
exposure will be between one panel and the next.