A helmet without rotational impact protection will still meet basic safety certifications and protect your head from direct, straight-on impacts. However, most real-world ski crashes involve angled falls — you don't hit the snow perfectly flat. Those oblique impacts create rotational forces that cause your brain to twist inside your skull, which is a leading cause of concussions and traumatic brain injuries.
Helmets without a dedicated rotational system like MIPS, Koroyd, or WaveCel rely solely on EPS foam, which isn't designed to address that twisting motion. You're getting linear protection only, which leaves a significant gap in your overall safety.
The price difference between helmets with and without rotational protection is usually modest — often $30–$60. Given that this is widely considered the most important safety advancement in helmet technology in recent years, it's worth spending a little more. If budget is tight, look for last season's MIPS-equipped models on sale rather than skipping this feature entirely.