When you download a file from a server without a VPN, there’s a chance you will encounter network congestion, most likely on your nearby ISP network or at the download server itself. When you use a VPN service, you add a third potential bottleneck to the route. Whether because of server load or congestion on the network surrounding the server, there’s a higher chance that your speed will be affected while connected to a VPN.
That attitude to the safety and privacy of personal data creates an enormous online security risk. Public Wi-Fi networks, which are ubiquitous and convenient, are unfortunately also highly convenient for attackers looking to compromise your personal information. How do you know, for example, that "starbucks_wifi_real" is actually the Wi-Fi network for the coffee shop? Anyone could have created that network, and they may have done so in order to lure victims into disclosing personal information over it. In fact, a popular security researcher prank is to create a network with the same name as a free, popular service and see how many devices will automatically connect because it appears safe.