Yellowfin doesn’t actually do much querying work, it sends off the query to the database where the data resides, the database runs the query and sends the result set back to Yellowfin. Yellowfin simply presents the request to the browser (with some additional formatting, charts, etc).
If your data resides on a machine that meets performance specifications, in a schema that is aggregated and indexed properly, your reporting solution will run well. However, while saying this there are multiple caching options within Yellowfin that are available to increase data performance.