Having sections/Watchlists collapsed by-default could be very useful for faster page-loads, reduced server loads and clearer pages.

This would mainly be used in combination with the multiple watchlists feature so that some watchlists can be hidden (collapsed) by default.

You can then often and easily refresh the page and have shorter pages but can still see other watchlists with the click of a button.

A way to quickly jump between watchlists (like between the enWP and WMC watchlist) would be useful too – for example as a TOC (maybe incl a counter of unseen items that were changed) but this is not part of this issue and just a note (maybe I'll create a new issue about this once having thought more about potential ways this could be implemented).