This applies across all sorts of situations. I get a lot of IMs from co-workers, for example. Normally I don't notice their impact much, since I have two big monitors worth of screen real estate and I can switch back and forth between IM windows and coding or testing quickly. But with less screen space (1280 x 800 instead of 3840 x 1080), the IM windows take up more space and I have to move them around frequently, which takes up more time.
Also, with slow internet connections, actually switching between windows is sometimes difficult, as redrawing a bigger chunk of the screen causes the whole connection to freeze for as long as several minutes at a time. And as upstream bandwidth is always more limited than downstream, sometimes my typing or clicks don't get transmitted for extended periods of time. It's very frustrating, to the point where I'm planning to get a mobile internet solution of some kind very soon. The travel has also cost me quite a few mobile phone minutes, as I can't use VOIP over the sketchy internet connections.