Why is it that I need to Refresh

q]] In the following link http://help.sap.com/saphelp_46c/helpdata/en/d3/2e974d35c511d1829f0000e829fbfe/frameset.htm

please find Formatting Data Using Nested Internal Tables

q]] Why is it that I need to Refresh WA_SPFLI-SFLIGHT ,& WA_SFLIGHT-SBOOK & Why I do not do the same with WA_SPFLI.