View the original community article here
Last tested: Jan 16, 2019
persist_for can be applied to PDTs, Models and Explores.
There is a significant difference between PDT persist_for and the model/explore persist_for (caching). PDT persistence controls how long should the PDT live on the DB as a temporary table after it was first queried in the explore. Model and explore persist_for controls how long should the query previously run in Looker be kept in memory. It's simply results caching. The two are completely independent.
When the persist_for parameter is set within both model and an explore, the explore setting will take precedence over the model setting. Check this Community article for more info