If you're like me, and came across this question when hoping to make a particular window have a fixed width (or height) without disabling 'equalalways'
and avoiding Ctrl-W=, you should be aware of 'winfixwidth'
(or 'winfixheight'
):
'winfixheight' 'wfh' boolean (default off), local to window
Keep the window height when windows are opened or closed and
'equalalways' is set. Also for CTRL-W_=. Set by default for the
preview-window and quickfix-window.
The height may be changed anyway when running out of room.
This is useful, for instance, in terminal
windows; I use setl wfw
in all of my vertical term-splits.