A standard heel cup is a basic molded design that relies on the shoe's overall fit and how snugly you dial in the closures. For casual riding, commuting, or recreational spins, it's usually perfectly adequate — if the shoe fits your heel shape well to begin with, you won't notice any issues.
However, if you're doing harder efforts like sprinting, climbing out of the saddle, or racing, a standard heel cup may let your heel slip on the upstroke. That movement wastes energy and can cause hot spots or blisters over longer rides. Riders with narrow heels are especially likely to experience this problem.
The key takeaway: don't just overtighten your whole shoe to fix heel slip. If your heel lifts during hard pedaling, look for shoes with reinforced or adjustable heel retention instead — they solve the problem without crushing your forefoot.