Yes—manual focus override is useful even if you select the AF point yourself. Its main value is speed and precision when autofocus is close but not quite right, or when AF struggles.

Common situations where it helps:

• low light or low-contrast subjects, when AF hunts or fails
• macro work, where depth of field is extremely thin and tiny focus changes matter
• flat subjects like documents, where you want to fine-tune focus across the frame
• any time you want a quick final adjustment after autofocus locks
• when changing AF points would take longer than simply tweaking focus manually

A popular workflow is back-button AF: leave the lens in AF, use the back button when you want autofocus, and just turn the focus ring when you want manual control. That way you can autofocus first, then immediately fine-tune without touching the AF/MF switch.

For the most exact manual focus, live view with magnification is especially effective, though it can be slower.