Essentially, this task would execute a T-SQL stored procedure to find the dimension key in the table and insert an inferred member if it is not found. The primary benefit to this is being able to avoid the case sensitivity of the SSIS engine and instead have the matching logic be executed in SQL Server. The row is then dispatched to the 2nd Pass Lookup.
The 2nd Pass Lookup is a Lookup transform identical to the initial attempt to find a matching dimension member, except with reference set caching disabled. This allows newly added rows, inserted by the Add Inferred Client Member task, to be part of the dimension lookup. If for some reason the candidate row is not found at this stage (perhaps an error getting the inferred member inserted was not caught), the row has an ErrorReason column added via a Derived Column transform, and is sent into an error flow. All inbound rows that find a dimension surrogate key in the 2nd Pass Lookup are moved into the destination (ie Production) fact table.