Enabling tab-bar-mode grows the frame's height (not always, just the first time). Disabling the mode does not shrink it. Is that intended?
(let ((initial (assq 'outer-size (frame-geometry))))
(tab-bar-mode 1)
(tab-bar-mode 0)
(list (assq 'outer-size (frame-geometry)) initial))
=> ((outer-size 689 . 687) (outer-size 689 . 671))