"Distributing the organisms by rotating the spreader rather than the plate tends to cause more pooling of the inoculum." https://asm.org/ASM/media/Protocol-Images/Preparing-Spread-Plates-Protocols.pdf?ext=.pdf
1 Answer
$\begingroup$
$\endgroup$
Forming a pool (second definition in link); forming a small amount of liquid on a surface. A la "I knocked my cup over and the coffee formed a small pool on my bench"
Basically this results in a concentration of the organisms in one area, rather than an evenly distributed spread.