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What am I losing by not using the C# Dev Kit?
(programming.dev)
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Unless you're part of a large enterprise, you're not missing anything you're likely to care about.
VS Professional does some counterintuitive magic for handling big related sets of related projects. It's particularly valuable if one has been cursed to work with old school C# XML SOAP web services.
You're also missing out on strong support for some other awful proprietary data connector libraries.