I have two suggestions for new features:
For privacy, it would be very handy to be able to hit control+L (or similar) to clear the screen, since I often leave signal running on my office machine.
All of my signal chatting is with one person (spouse!). It would be great to be able to hide or shrink the contact list on the left side of the UI so that only the conversation is visible. For now, I slide the window to the left edge of the screen to achieve this.
[Third request now moot -- thanks!] @scottnonnenberg kindly pointed out that deleting a contact is already possible, via the "delete messages" menu item for the conversation. This is handy because some people in my iOS contact list are people with whom I never intend to signal.
Regarding your second item, on version 1.0.39 and above you should be able to select that user, then select 'delete messages' in the top-right menu. That should make the contact go away.
A key shortcut to delete conversations would be nice. Also a "boss" shortcut could be interesting.
Since this is a privacy-focused messaging platform, it would be really nice to have all these features in the desktop (in a similar way the previews can be hidden in the multitasking on iOS, just to say).
I've created a pull request https://github.com/WhisperSystems/Signal-Desktop/pull/1904
where the conversations can be closed. The contact list will still be visible though.
adding a possiblity to hide the contact list would be great ...
adding a possiblity to hide the contact list would be great ...
yeah, i often use signal & some other apps side by side (usually signal is on the right 1/3 of my screen & main app on the 2/3 on the left) on my laptop. And i only need the active conversation, not the contact list, so hiding it completely or at least reduce it to profile pictures would be very nice !
The matrix client Element (previously riot.im) has a nice solution for the second bullet. You can directly modify the width of the sidebar. If you shrink it (or the window) below a certain width, the sidebar collapses to be icons only. I'd love to see the same behavior in signal.

+1 for hiding contact list
About hiding contact list, see https://github.com/signalapp/Signal-Desktop/issues/2454
A good workaround: https://github.com/signalapp/Signal-Desktop/issues/3433
Keep in mind the total width window is still constrained to total width as if the full list was present, so no way to make chat skinny/slender/tall, even when making gutter 75px.
+1 for hiding or collapsing the contact list
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adding a possiblity to hide the contact list would be great ...