Problem using increment parameter with the token renewal rest api

While using the Vault rest API for the token renewal, the parameter “increment” used along with the “accessor” does not seem to set anything on the lease duration or period of the token.

If I am misinterpreting the use of parameter “increment”, could I get a better definition of how to set a specific period while renewing a token or is it rigid in the sense that the period initially set while creating the token will forever be carried for every renewal of the token.