Database sharding: horizontal versus vertical

been thinking about database scaling lately, we all know sharding is key for large datasets, but there are a couple of main ways to go about it. horizontal sharding splits tables into multiple databases, and vertical sharding splits columns into different tables. each has its own set of pros and cons depending on the access patterns and data structure. what are your go-to strategies for deciding between the two? any war stories or best practices you can share. curious to hear how others have navigated this