You've already beaten the game in English, or the English dub is notoriously terrible (looking at you, early Arc Rise Fantasia ).
If you want the absolute raw, original director's cut of a Japanese game—warts, cultural references, and all—an undub is indispensable. However, if you value convenience, menu cohesion, or actually like the English voice cast, you should skip it. You've already beaten the game in English, or
You're a casual player, hate tinkering with files, or the game features a genuinely great English cast (e.g., Dragon Quest VIII , FFXII ). and all—an undub is indispensable. However
The undub community keeps gaming history alive. But remember: a perfect localization shouldn't need an undub. Use this tool as a scalpel, not a sledgehammer. if you value convenience