Reinforced ladder straps are thicker, tougher versions of the toothed strips that feed through your binding ratchets—the parts that tend to wear out first on any binding. They're built to resist stripping and general wear better than standard nylon or polyurethane straps.
For most riders hitting the mountain 10–30 days a season, standard straps are perfectly adequate and typically last a few seasons. But if you ride 50+ days a year, charge hard in freeride terrain, or have a habit of cranking your ratchets down aggressively, reinforced straps are worth seeking out. They'll hold up longer and lower the odds of a strap giving out on you mid-run.
You'll usually find reinforced ladders on premium and freeride-focused bindings. If you're tough on gear or just want one less thing to worry about, it's a smart feature to look for—especially since ladder straps are the most replaced binding component out there.