Tree Style Tabs, Sidebery, or similar are must-haves. I do try to clean up my tabs regularly, but I almost always have more open that can conveniently be displayed in a horizontal tab bar.

Vertical screen real estate is at a higher premium in general on desktop, anyway. No point in keeping my browser at the full width of my screen when most sites adamantly refuse to use the space anyway (case in point: Lemmy).