Originally Posted by
rpenmanparker
Shimano and SRAM generally recommend threading the chain from the big ring to smallest cog going through the RD, then just join the chain exactly at the measurement that makes the line through the two RD jockey wheels as close to vertical as possible. This method is not much recommended by the knowledgeable folks here, and they cite good reasons for their rejection of this method such as little forgiveness for a bigger cassette. ...
Any of a number of methods will work fine when operating within the capacity of the RD, where there's a working range between the minimum and maximum length.
However issues can occur when running at or slightly over RD capacity, where chain length can become critical with little or no room for error. That's when checking the minimum length becomes important.