As a best practice, upgrade deprecated panel sets to screen layouts. Existing panel sets continue to function, but you cannot create a new panel set in applications rendered in HTML 5 document type (standards mode). Screen layouts are available only to user interfaces rendered in HTML 5 document type (standards mode).
Caution: Prior to updating a panel set, make sure that the screen layout that you select contains regions that correlate to the areas in the existing panel set. If an existing panel set area does not correlate to a region in the screen layout, it will not be retained on upgrade.
For instance, if you want to update a Header Left Right panel set, select the Header Left Right screen layout, to ensure that all sections in the panel set display in the new screen layout.