Practical examples of Threshold Secret Sharing?
I worked on a secure document management project 20 years ago which used secret sharing. It is widely used in financial networks. Actual use cases with public details that are easily accessible include: 


Threshold key sharing is used in Hardware Security Modules, for example to unlock the administrator account. In the Amazon CloudHSM documentation, this is explained in detail: 
Amazon CloudHSM: About M of N
Hashicorp's Vault uses Shamir's Secret Sharing during the "unsealing" process as explained here: (https://www.vaultproject.io/docs/concepts/seal.html) This enables reading and decrypting secrets from the storage backend.