shut off valve
 

Is there any good reason to put in a shut off valve for my water leaving the display tank into the sump tank...

I am definetly going to put in a shutoff and a union for disconnect from my sump pump to the DT ....

If you are setting up a Herbie overflow you are going to need a shutoff valve, to regulate the water in your overflow box,

I have valves on every line, you never know when you are going to need them. Easier to do it when setting up, rather than trying to add later.

not really needed on the drain.

For pumps, handy a valve on both sides.

I will have to agree because i do have a valve on all my lines.
only because its an inwall tank,otherwise i wouldn't.