Bandwidth—the number of bits per second that a device or connection can transfer every second—is the number that everyone loves to talk about. Whether it be the gigabit per second that your Ethernet card does, boasting about your fancy new FTTP Internet connection at 85 megabits per second, or bemoaning the lousy 128 kilobits per second you get on hotel Wi-Fi, bandwidth gets the headlines.
Bandwidth isn't, however, the only number that's important when it comes to network performance. Latency—the time it takes the message you send to arrive at the other end—is also critically important. Depending on what you're trying to do, high latency can make your network connections crawl, even if your bandwidth is abundant.
Why latency matters
It's easy to understand why bandwidth is important. If a YouTube stream has a bitrate of 1Mb/s, it's obvious that to play it back in real time, without buffering, you'll need at least 1Mb/s of bandwidth. If the game you're installing from Steam is about 3.6GB and your bandwidth is about 8Mb/s, it will take about an hour to download.
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via http://arstechnica.com/information-technology/2013/03/youtube-buffering-or-slow-downloads-blame-the-speed-of-light/
