Well, the Marquee stripe is similar in use to the Marquee Tool.
You can use the Marquee stripe to select multiple regions and parts of regions easily.
drag across the Marquee Stripe to create a selection within the regions across all tracks.
You can de-select a region on one track by clicking on that track header.
By clicking within the highlighted marquee area on any of the regions all regions will be cut within the Marquee stripe.
By pressing Cmd-C (copy) and moving the playhead to a new location and pasting (cmd-V) you can easily copy and paste parts from within regions without cutting the regions. This can be very useful if some of the regions are looped and you only want to copy say one bar's worth of the arrangement to a new part of the project.
It's also a quick way to use Autopunch for recording...
Also, brilliant for automation if you want to place four nodes (two on either side of the selected marquee stripe) on the selected track.
There must be more good uses...
If anyone has any other ways in which they use the Marquee stripe, please do share the knowledge ;-)