It is safe to delete set free variables?

For example I have followins line of code (usually I get these code from answers).

(projectile-global-mode)

; smerge-mode
(setq smerge-command-prefix "C-cv")
(setq undo-tree-show-minibuffer-help t)
(setq undo-tree-minibuffer-help-dynamic t)

For each (projectile-global-mode, smerge-command-prefix, undo-tree-show-minibuffer-help, …) I am having following warning: assignment to free variable. As I understand free variable does not have any affect on emacs’s setup.

=> Is it safe for me to delete them?