Why to empDir in elasticsearch and kibana

I am using ECK 1.1.0 , I am not defining anywhere in elasticsearch or kibana yaml files for empDir. But after deploying in kubernetes , when I describe pod I can see the below:

- emptyDir: {}
  name: elastic-internal-elasticsearch-config-local
- emptyDir: {}
  name: elastic-internal-elasticsearch-plugins-local
- emptyDir: {}
  name: elasticsearch-logs

kibana

- emptyDir: {}
  name: kibana-data
- emptyDir: {}
  name: elastic-internal-kibana-config-local

why we are using empDir for those?

What type of data they were storing. Can we pvc instead of empDir?