Hi Karthikeyan,
CO point ofview, WIP and Variance GL accounts should not create as Cost elements. The reason is: In case of other GL accounts, values will be flow from FI to CO. So, need to create all other GL accounts have to be created as CEs.
But, in case of WIP and Variance, values will be flow from CO to FI. So, no need to create as CEs.
Ultimately, we create cost elements when values flow from FI to CO.
Usually, COGS is not a cost element but in case of tracking all the cost on sales order level, we create COGS as a cost element.
Hope this helps.
BR, Srinivas Salpala