An expensive one, both in energy consumption and hassles! A single Firefox instance, with some (few) plug-ins, and the task viewer, in a common Windows 7 setup, provides an incredible 250Mb of RAM consumption. A single instance of a.... document viewer, with text, images and so on, consumes more than the entire Windows XP installation, with dozens and dozens of active processes like any operating system.
This says something of great importance, and without leaving the software engineering side and its implications. It's true that today there are memory sticks for sale of 8Gb or motherboards that setup the limit for RAM in 32Gb. Also that multiple people are using netbooks with very limited resources, or maybe older computers. In pretty recent times hundred millions of laptops were sold with 1Gb of maximum random access memory. For who doesn't know what this means, it's actually very easy: RAM is a very fast memory in comparison. If you don't have enough RAM the operating system tries to emulate it and this means slowness, a kind of that the user perceives for sure.
When you calculate the consumed energy about RAM in terms of hundreds of millions, it's a relevant figure that no one should take for granted in the current state of development and its global unsustainability. So, programming is (even with electricity coming from renewables as everything has a degradation ratio) an act of responsibility, not for children trying to compete with others creating a monster with voracious appetite growing each new year.
Functions, functions, but... how many are used by the 99% of the population? A new update could as well be simply based in this: it requires less resources to do the same. This last aspect is rather usual in the programming world and it requires more expertise than go irrational with the numbers, letting the river go wider, like a fish that looks to the surface without taking notice of its own environment.
However, something is happening right now when you convert a web page from Firefox or another alike browser to a format like PDF. Miraculously —well, to say something— the HTML document, appears then divided by a too high factor, and the PDF viewer at all consumes as three or four operating systems from a few years back like XP. You could have several instances of the PDF viewer without compromising the stability of the system nor leaving an impression of slowness in the overall response.