I am definitely a lover of "fast glass" because it offers more opportunities in a variety of shooting conditions, especially when the ambient light is not optimal. One can get some stunning photographs when using a fast lens in, say, a portrait situation where the subject is sitting by a window. No need for flash, which makes a huge difference. The problem, though, with using a fast lens "wide-open" at f/1.2, f/1.4, f/1.8 or f/2 is that the depth-of-field is affected. In portraits, it's best to focus directly on the eyes so that they will be sharp while everything else softens a bit....
A lot of times when shooting macro it is necessary to go into manual focus as opposed to auto-focus in order to get exactly the image you want. As mentioned, auto-focus does have the issue of needing some kind of contrasting line or area upon which to focus. With manual focus you can get exactly what you want.
ChrisA said:
On a Landscape I can manually set the lens at the "parafocal" distance which is just short of infinity. For macro work manual allows me to better choose which part of the frame is in sharp focus.
Never heard it called anything other than "hyperfocal distance" before....but, yes, this is something which can make a huge difference when shooting landscapes. It is easier to do the hyperfocal distance thing with the older lenses which have all the markings on them, as opposed to the newer lenses which don't.... There is definitely still a place for those older lenses in photography! Sometimes automation can carry things too far. With Nikon, being able to use older lenses on their modern cameras really is a benefit.