Coextrusion makes it possible to build film out of three, five, seven, or more layers, each one doing a specific job. That capability gets misused when buyers assume more layers automatically means a better film. The right number of layers is the number needed to solve the actual performance requirement, and not one more.
What single-layer film does well
A single-layer film, often a blend of one or two resins, is simpler to produce, generally lower cost, and easier to recycle because there is only one material to manage at end of life. For applications without a barrier requirement, without a need for a distinct outer print surface and inner seal surface, and without an extreme strength demand, single-layer film is usually the right answer and multi-layer would just add cost without adding value.
What multi-layer film solves that single-layer cannot
Multi-layer structures exist to let one layer do a job that would compromise another layer if combined into a single blend. A common example: an outer layer optimized for printability and stiffness, a core layer optimized for tensile strength or barrier performance, and an inner layer optimized purely for seal performance at a low initiation temperature. Trying to get one resin blend to do all three jobs well usually means it does all three adequately and none of them well.
Barrier requirements almost always mean multi-layer
If the product needs protection from oxygen or moisture transmission beyond what a polyethylene-based film can provide, a barrier resin like EVOH usually has to be sandwiched between structural layers, often with a tie layer to bond materials that do not adhere to each other naturally. There is no single-layer shortcut to high barrier performance with current commodity resins.
The cost and complexity tradeoff
Each additional layer in a coextrusion structure adds line complexity, more potential failure points in production, and incremental cost. It can also complicate recyclability if the layers use materials that do not separate or process together cleanly. None of that is a reason to avoid multi-layer structures when they are genuinely needed; it is a reason to avoid specifying them when they are not.
How to decide
Start by listing what the package has to survive and protect against: physical abuse, barrier needs, seal performance, and shelf appeal. If a single well-chosen resin blend can satisfy all of those requirements, use it. If satisfying one requirement well would compromise another in a single layer, that is the signal multi-layer construction is solving a real problem rather than adding unnecessary cost.