The Line Style List tab is added when you select a worksheet column of categorical values to control the Line tab line Style (i.e. you choose a worksheet column from that drop-down list).
By default, Origin uses the LabTalk list of Line Types. However, you can customize this list, rearranging or eliminating styles to suit your needs. Check the Use custom increment list box to expose controls and follow instructions on this page for customizing the list.