Users of popwin, which displays certain “temporary” buffers (e.g. Help, Messages, etc.) in dismissable pop-up windows, may run into some issues with Helm.

Many Helm sources bring up the Help buffer with persistent action. In a two-window configuration, the Help buffer is displayed in the other window.

If Popwin is used for Help buffers, however, the Help buffer will be shown in both the pop-up window and the other window. This is unnecessary and annoying.

You can turn off Popwin for Help buffers globally, but it may be preferable to turn them off only while using Helm.

“Turning off” should be done in helm-minibuffer-set-up-hook, while “turning on” should be done in helm-cleanup-hook. Issue #1386 describes why helm-exit-minibuffer-hook should not be used for “turning on”.

The following example works well:

(defun *-popwin-help-mode-off ()
  "Turn `popwin-mode' off for *Help* buffers."
  (when (boundp 'popwin:special-display-config)
    (customize-set-variable 'popwin:special-display-config
                            (delq 'help-mode popwin:special-display-config))))
(defun *-popwin-help-mode-on ()
  "Turn `popwin-mode' on for *Help* buffers."
  (when (boundp 'popwin:special-display-config)
    (customize-set-variable 'popwin:special-display-config
                            (add-to-list 'popwin:special-display-config 'help-mode nil #'eq))))
(add-hook 'helm-minibuffer-set-up-hook #'*-popwin-help-mode-off)
(add-hook 'helm-cleanup-hook #'*-popwin-help-mode-on)

This example is about Help buffers, but the idea of turning Popwin off only while using Helm applies generally.