Hi Jurgan, from the description for crop.m I gather it crops whitespace from a bitmap (i.e. non vector type) image file which is already saved to disk, e.g. a jpeg, bitmap, png etc. It does not appear to act on figures.
I suppose you could get similar functionality to tightfig by first saving your figure to disk in one of these formats, then running crop.m on it. I prefer the tightfig workflow personally.
Jurgen, most of the functions you mention adjust the space between and around individual axes in subplots, and at least some have to be called on creation of a subplot. tightfig crops the white space around the outside of all the axes (and legends) in any figure without adjusting the rest of the plots at all. tightfig also identifies if you have a 3D zoomed axes in your figure and ignores it, since such figures cannot be cropped. tightfig is also well commented so you can understand it's workings.
Actually you failed to identify the one other function on the file exchange I know which does also have this functionality, export_fig.m.