Thanks for the information. I just tested a quick resnet training on ImageNet using 5 workers vs. 0 workers on an AMD EPYC 7742 64-Core Processor and see that the 5 workers use:
--total-cpu-usage-- -dsk/total- -net/total- ---paging-- ---system--
usr sys idl wai stl| read  writ| recv  send|  in   out | int   csw
 12   1  86   1   0|   0    32k|  31M 2301k|   0     0 |  81k   86k
[...]

while no additional workers (loading in the main process) uses:
 3   0  97   0   0|   0    56k| 259k  303k|   0     0 |  13k   14k
[...]