The memory usage of the Check_MK check helpers, especially the growth that occures during runtime, has been reduced significantly.
One example which has been measured in a single site with 30 Check_MK check helpers configured and a large configuration (a lot of hosts, services, tags and rulesets):
Before this change it was executing 1000 service checks per second with a total memory usage of about 15 GB.
After this change it is now performing 1100 service checks per second with a total memory usage of 3.5(!) GB.
The exact memory reduction highly depends on the Check_MK configuration, but should be measurable in all medium to large environments.