Whether winning a snippet increases or cannibalizes your clicks comes down to one thing: how completely the snippet answers the query. A snippet that completely satisfies a simple query tends to cannibalize clicks, because the user gets what they came for inside the results and never visits the page, which is the zero-click outcome. A snippet that only teases a complex answer tends to increase clicks, because it establishes you as the source and prompts the user to click through for the depth the box could not contain. Same feature, opposite effects, split by how much the snippet finishes the job.
The pivot is satisfaction versus tease. Take a query like a unit conversion, a definition, or a single date. A snippet answers it outright, the user reads it in the SERP, and there is nothing left to click for. Winning that box can quietly cost you the visits you would otherwise have earned from a high rank. Now take a query about how to do something involved, or a comparison with real nuance. The snippet can show the headline answer or the first steps, but the full procedure, the caveats, and the reasoning live on the page. The box advertises your authority and pulls the click, so the snippet works as a billboard rather than a substitute.
This is why “snippets always increase traffic” is the wrong default. Whether the box helps or hurts is not a property of snippets in general; it is a property of the specific query and how completely the displayed passage resolves it. Zero-click behavior is also a moving target as Google adjusts what it shows in the SERP, so it is worth confirming against your own click-through data rather than assuming.
Before you chase a snippet, judge the query honestly. If a complete answer fits in the box and leaves nothing to click for, the snippet may cost you visits, and a strong organic position could serve you better. If the full answer needs the page, pursue the box and treat it as a click magnet. Check your search-performance data after you win it to confirm which way it broke.