if you use the old style nft top plates that look like brick work, then spreader mat helps as these are shit imo
they often keep the stream too deep, the brickwork pattern does not spread out the stream very well
when plants are large they can grow so many roots that the stream cant flow under the root mat
NFT was not designed to work with spreader mat, its just used in these systems because of the initial poor design also if the pump fails the spreader mat helps keep the roots moist until you notice the pump has failed , i always put two pumps in all my systems in case one fails and i do not notice, also having the stream run from two points helps spread out the solution even further
the spreader mat also gives the roots something to bite into, and it can be used to "train" the roots to grow in the direction you want
the down side is spreader mat holds a fair amount of water that keeps the roots too wet imo and it causes the flow of the solution and the roots to clump up in places
spreader mat is more likely to cause puddles and disrupt the flow than no spreader mat
spreader mat also makes the root mat thicker, which helps in small systems but in large systems its best to keep the root mat as thin as possible
the roots will mat into themselves perfectly they do not need spreader mat to do this
the ideal situation imo would be to put a single plant in the center of a 1m2 with the diamond shape top plates
these newer top plates are better they keep the flow shallow compared to the brickwork ones
i normally put a 1 inch thick piece of wood under them to increase the slope this keeps the stream perfectly shallow
i do not want the root mat under the solution completely, its good to have about 30% of the root mat thickness sitting in air with the stream running under
a single plant in the center of this would have 3ft in every direction for the roots to spread out
90% of the roots could stay on the top plate virtually none will grow into the res
the thinner you can keep the root mat the more surface area the roots have in direct contact with the flow/stream, also a shallow stream spread out over a larger surface area allows for more oxygen to enter the stream as it flows
peace
