"Refurbished" covers a wide range of actual condition, and that range is the most important thing to understand before you buy.
What "refurbished" usually means
A refurbished unit has been used, returned to a seller or lessor, tested, and in most cases had any failed components replaced. It is not the same as "used" in the sense of buying something off a resale marketplace with no testing behind it. Reputable sourcing includes a functional test pass and a stated warranty — if a seller can't tell you what was tested and what the warranty covers, that's a sign to ask more questions, not a reason to assume the worst.
What changes, and what doesn't
Performance doesn't change. A refurbished switch or server runs at the same spec as it did new — clock speeds, port counts, and throughput are fixed by the hardware, not by how many previous owners it had.
Warranty does change, and this is the part worth reading closely. New hardware typically carries the manufacturer's standard warranty. Refurbished hardware carries whatever warranty the seller offers, which may be shorter, may come from a third party instead of the OEM, and should always be stated clearly before you order.
Cosmetic condition can vary — light scuffs on a chassis are common and don't affect function. Ask for photos if this matters for your environment.
Lead time is often shorter for refurbished units, since they're not waiting on manufacturer production and shipping.
When refurbished makes sense
Refurbished is a strong fit for lab and non-production environments, cost-sensitive branch deployments, hardware that's being added to an existing fleet of the same model, and any situation where the warranty terms on offer meet your actual risk tolerance.
When new makes more sense
If you need the longest possible warranty runway, you're deploying a brand-new product line where refurbished stock doesn't exist yet, or your environment has a strict new-hardware-only procurement policy, new is the right call.
The bottom line
Neither option is inherently the "right" choice — it depends on your warranty needs, budget, and timeline. Ask for the condition and warranty terms in writing before you order, for either option.