Large volume means number of rows and data size of source(s) that need to be processed into the target system by applying good amount of complex validation/filtration/transformation logics. The "Number of rows" and "good amount of" in the previous sentence depends on the hardware capacity and availability of ETL time window of individual systems. Before considering the idea discussed in article, study need to be done on the project for facts like current/future hardware capacity, how much data parallelism can be applied with current hardware, current/future available time window for etl processing, future complexities in validation logics, etc.