Intercoats are not always necessary, but you can use intercoats at any time. For example, intercoats between candy coats are necessary, and different intercoating material may be necessary to prevent bleeding. Another example is the use of chrome paints. For years we have been trying to get a chrome paint that would work, and they always went gray when we clear coated. Now Engineered Angler on YouTube has discovered that Minwax Polyacrylic and pledge used as an intercoat stops the gray and keeps it glossy/chrome.
On the other hand, using intercoats between normal opaque or transparent coats is totally unnecessary. It just adds thickness and weight that is not needed, and not always wanted.
Finally, if the intercoat is compatible with other paints, I do not sand or remove the shine at all.