Booster Straps are probably the best thing you can do for your day's skiing. The idea itself is, as the best ideas tend to be, remarkably simple. Adding elasticity to the power strap of the boot to allow for dynamic forward pressure while retaining lateral stability. Designed to increase performance in race boots, the straps were quickly found to reduce shin and calf bang for all types of skiers and, in particular, for park skiers. The elastic properties of the strap help keep the boot cuff and/or tongue (depending on boot style), in constant contact with the lower leg. On landings, that reduces the level of impact generated by the boot and leg moving at different rates.

As skiing progressed, more benefits revealed themselves. In any situation where the boot and leg might naturally flex differently, Booster straps help ease the side effects. Buttering is perhaps the most instantly noticeable. You can instantly feel the difference compared with a regular power strap, with the Booster strap adding more control... and reducing pain. The same is true when it comes to tackling mixed conditions when freeriding. The constant contact between the boot and leg helps to create a more locked-in feeling while contributing to the rider's ability to adapt to changes in snow conditions. It also dampens the jarring effects of bumps and ruts.

https://www.newschoolers.com/videos/watch/1100382/Booster-Wide-mp4
Long story short, the entire NS staff runs Boosters on all our boots. We think they are just as essential as footbeds and well-fitting boots in improving the park skiing experience. They feel like a small change, but they help you ski better and for longer. The only thing to do is to choose a flex. In general, for park and freeride, we feel like the Expert strap is sufficient for most skiers. The smaller, stiffer elastic patch on the World Cup Strap delivers more edging power but does less to reduce shinbang and increase dynamicity than the Expert strap. So we'd mostly recommend the World Cup for bigger skiers or perhaps those looking towards comp-style freeriding. For all the rest, Experts (or even the Intermediate for lighter pure park skiers), are likely the way to go.