Difference between --checksum & --ignore-checksum?

Hello experts,

I am using Rclone v-1.63 in remote (api) mode.

Using '/sync/copy' & '/sync/move' end points -
Trying to understand the difference between ' --checksum' and ' --ignore-checksum'
(Referring - Global Flags)

Is checksum not enabled by default?
Should we enable with '--checksum'? if so what is the use of '--ignore-checksum'?

Could anyone please help me to understand this?
Thanks in advance.

Thanks,
Mahendra

All is explained in docs:

--checksum

--ignore-checksum