It depends on the exchange. If the exchange is honest and doesn't mess with any numbers, then it provides users with ease of access to the market. When users have ease of access, they can trade more. More trading means higher liquidity and better transactions. If more traders have access to decentralized exchanges and can move money back and forth, it will increase the value of cryptocurrencies.

But if the exchange has unethical practices like selling info, opening itself to hacks, or faking volume, it can affect crypto very negatively. Hacks especially are very bad news for crypto because they generate fear.