Is there anything you can do in XSLT that cannot be done in Linq for XML?
No, because LINQ to XML is the API used by the Turing programming languages and covers more XML Infoset than the XSLT document model (for example, you can completely control the difference between text and CDATA nodes in L2X).
How important is learning XSLT?
Depending on what you do. In general, yes.
When do you pick one over the other?
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