These functions create temporary files that can be used in calls to qgis_run_algorithm() or elsewhere. These files are created in a special temporary directory (qgis_tmp_base()) that should be periodically cleaned up using qgis_clean_tmp(). You can set your preferred vector and/or raster file extension using options(qgisprocess.tmp_vector_ext = "...") and/or options(qgisprocess.tmp_raster_ext = "..."), respectively.