This panel displays an alternative view of items selected in the main display. As you know, mammalian genes are often enormous - spanning vast regions of the genomic sequence - and comprised mostly of intron sequence. The sliced view aims to give you a higher level summary of gene structures by trimming out a lot of the intronic regions and allowing you to focus on what most of us consider the most interesting parts: the exons. (Of course, scientists investigating introns and splicing signals would no doubt consider the introns to be just as interesting!)
The following image shows how this works. The top panel is the IGB main display window shows the normal, non-spliced view of a region containing what appears to be two overlapping genes from a cow: GBN4, which contains an enormous five prime that completely encompasses another gene, ZNF639, which encodes a zinc finger protein. The Sliced View panel on the bottom shows these same two genes, but with much of intronic sequences sliced out. The places where the slices were made appear below the axis in the Sliced View.
Note how the sliced view makes it easy to see both gene structures simultaneously, whereas in the main view ZNF639 is so small it is impossible to even see the number of exons it contains.
Also, see [Showing ORFs and stop codons|../display/igbman/Showing+ORFs+and+stop+codons|] for more uses of the Sliced View Panel.