To add a little bit of background to the other answers, one has to remember that network latency can vary significantly, and can impact a user's experience.
One of the most obvious sources of network latency is distance: the signals that carry your data travel at more or less the speed of light, so the longer the distance travelled from client to server, the higher the latency. Communication between two computers linked by an Ethernet cable will take a few milliseconds. Communication with a server across an ocean will take dozens or hundreds of milliseconds. Communication that goes through a geostationary satellite will take hundreds of milliseconds.
This is clearly visible when doing a ping, which measures the round-trip time, which in this case is very close to the sum of the latency in both directions.
A few other things that have an influence on latency:
- the number of links/hops: in most cases, a packet needs to be fully received before it can be sent on the next link. That adds a bit of latency on each hop;
- the throughput of those links: the slower the link, the longer it takes for the full packet to go through, and thus to be forwarded on the next link;
- the load of those links: if a link is full, the packet may have to be queued until it can be sent;
- for links with local retransmission, the error rate on the link: the higher the error rate, the higher the chances the packet may need to be resent.
Latency can have a strong effect on the user experience (or not):
- the best known case is the latency affecting players of MMORPGs and other online games.
- anything interactive where the interaction is controlled on the other side is affected by latency. Telnet/ssh, remote desktop, are all affected by latency.
- voice communication is affected by latency, and with high latency you end up with people interrupting each other all the time.
- older file transfer protocols also suffered from latency as they did not implement sliding windows, and the sender had to wait for the packet to arrive at the destination, and the acknowledgement to come back, before sending the next one.
Even with non-interactive cases, latency can have an effect (which is illustrated in the OP's example): when there are lots of small files to download, latency can result in a higher total load time if the protocol has to wait for one file to be completely downloaded before starting the download of the next one, compared to a protocol which would allow multiple requests to be sent at once, and the responses being sent with no interruption between successive files.