I haven't been able to find a definitive source whether the mobile Signal installation can be abandoned (or removed altogether) after setting up the account in the desktop application.
In the Android battery statistics the Signal app has contributed some percents of the overall power drain, additionally as a keyboard-preferring user I'd opt for moving exclusively to the PC build.
I plan keeping the app around in a (paused) Android work profile, for now. The Signal PIN code has been saved to my encrypted password database and don't have plans to change my phone number.
Note that this superuser.com question is about creating an account without a smartphone — which isn't supported.