[Jos]

Hi Manpreet,

The external ID option can be used for automated lookup and to be used as reference in other systems. Within each org record ID's are generated. So when you import data within a dev sandbox you can't import the ID values as there are generated by salesforce. However, the external ID does not get (re)generated.

So this means when you import contacts using the external id on account, using the right tools will perform the lookup. This will save you lot's of time.

There's a whitepaper you can download on this subject here: http://salesforcesquad.eu/homepage/prepare-your-production-for-sandbox-dataset-deployment/

[Jos]

Hi Saurabh,

I believe because of inconsistancy risks as users  (OwnerID) are the core or all objects.

Cheers,