i find it highly annoying if pages show different content on the same url. many bad sites with javascript do not update their url.
javascript is often used for no apparent benefit. my favourite (or shall I say anti-favourite) are websites that, when I click on an image thumbnail darker the main site, show some animation and then showing the bigger image. I have experienced it many times that disabling js would directly serve me the image and do so much quicker.
some online store I use pops up details for items when I mouse over. each time changing mouse focus. I can not get a simple list with all the details to use my browsers search function with. it also has no pagination but autoloads more items on the bottom. if I revisit the page (eg after looking at an image) I have to start at the beginning again.
javascript allows website to screw with my copying. hover the mouse on a Google result, the status bar shows the proper target. rightclick and copy to get some redirection shite instead.
phew, where do I stop...
disabling js also implicitly removes a lot of advertising, pop-up windows, always scrolling bars. when I have to use someone else's computer I often cannot understand how they stay sane.
Google steals my focus, I use backspace to navigate "back". on Google that leads to me removing characters on the search and the search automatically updating and adding more pages to the history to navigate back through.
javascript often leads to sites eating my CPU. I value my battery life and CPU temperature.
I use reddit a lot on a unreliable connection. I often happily vote, just to see later that javascript pretended my votes counted while in reality they never arrived at the other end.
javascript can be great for thing but it gets abused so much that disabling made me enjoy the web much more. if something does not work, well, chances are I was procrastinating anyways and won't miss anything important by closing the tab. I did not install flash for the same reasons.
if I have to enable js for something it is two keystrokes (in opera). I can also enable it per site very easily.