Listings add access, and access adds buyers who previously could not participate. The announcement move is usually the largest part, sometimes tens of percent within minutes, with the actual listing day frequently weaker as early holders finally have somewhere deep to sell.
Structure matters more than the headline. A listing on a venue with real order books and market makers improves market-depth-crypto durably; one on a small venue changes little. Front-running of listing announcements has been prosecuted as insider dealing in at least one US case.
The first hours trade badly. Reference prices are unreliable, spreads are wide, and initial candles often wick violently in both directions. None of this implies a listing is a reason to buy; it describes why the price behaves the way it does around one.
Related: delisting-crypto, market-depth-crypto, exit-liquidity, cex