A slight restriction rating means you'll feel minor resistance when you bend your knee all the way, but it won't interfere with your normal skiing movements. Think of it like wearing a slightly snug sleeve—it's noticeable at full flex, but not when you're making typical turns on the hill.
This is actually the sweet spot for most all-mountain and freeride skiers. You get noticeably better impact protection than an unrestricted pad, without sacrificing the mobility you need to ski naturally. The trade-off is worth it for anyone skiing variable terrain, trees, or bumps where knee impacts are a real possibility.
The key is to test the full range of motion before you buy. Do a deep knee bend and a skiing tuck—if the resistance feels manageable and doesn't throw off your balance, you're good to go.