Buying separates instead of matching sets gives you one obvious advantage: you can size the top and bottom independently. But the bigger benefit is what you can do with just a few pieces.
Three tops and three bottoms is nine combinations, not three. Each pairing reads differently enough that nobody's counting. A solid top with a print bottom looks different from a print top with a solid bottom, even if you're working with the same four pieces. You get a full week of distinct looks from two or three purchases.
For color mixing, the reliable rule is a neutral paired with a print. A white or black top with a patterned bottom works nearly every time, and the reverse does too. Two prints can work if they share a base color — a floral and an animal print in similar tones read as intentional rather than accidental. Two solids are the easiest: analogous colors like terracotta with coral, or a warm paired with a neutral like rust and cream.
Coverage doesn't have to match between top and bottom. A fuller triangle top with a minimal bottom lets the top do the visual work. A bandeau with more coverage below flips that. There's no rule that the pieces need to carry equal weight visually.
Our tops and bottoms at Melancia are sold as separates for exactly this reason. The Pedra do Sal top comes in several colorways — pair it with a solid bottom and you have multiple distinct looks from one top. The same logic applies to the Grumari Sol and the Ipanema Luz. The more separates you have, the more the math works in your favor.