Using the custom fields as the stock location requires modifying the code so they show up in the admin orders page, packing lists, etc... in addition custom fields are not searchable.

Stock location is a basic requirement for Ecommerce and adding this field so it is part of the product details would be of huge benefit and would provide:
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More Comprehensive Packing List
Better inventory control
More Efficient stock picking
Improved integration with third party inventory systems or add-ons
Keep up with solutions from competing providers
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John