Usage of other primary keys than SugarCRM GUIFD

Good Morning,
I have an ongoing discussion with some of my colleagues regarding the usage of the standard GUID SugarCRM uses as the Primary Key of records.

We are all new to SugarCRM and I managed anyway to get all CRM data from our old system into the new SugarCRM instance.
In the old application companies and contacts have IDs known for example in external campaign platforms.
My first thought was using all the old legacy IDs as IDs in SugarCRM. I did that and everything was pretty easy including a M2M link between Opportunities and Contacts by using the Sugar API that expects the IDs of the records to link them.

Now some colleagues are saying that the usage of the GUID is recommended and it is not recommended to use other values as the PK.
This has been mentioned during a training my colleagues joined and SugarCRM support replies the same.

I'm working with CRM systems and databases since a very long time. My experience tells me that I can use any key values I want.
But I have to make sure that the values have a length that fits into the PK fields
Also it must be 100% sure that no conflict between the old IDs and SugarCRM generated IDs could ever happen.

Is there anything I'm not aware of that is special in SugarCRM. And I'm not talking about changing existing GUID values in the application.
I'm only talking about the usage of legacy IDs as SugarCRM IDs for a one time data migration.

Thanks a lot in advance
Michael