I doubt many people would change cassette based on occasion, but I suppose it is possible - it isn't too onerous a task to swap a cassette out. But certainly I (and I suspect others too) will fit a cassette once and it will stay on the wheel for its lifetime.
I think the key thing with a cassette choice is basically how close (in terms of number of teeth) adjoining sprockets are to each other.
In one of the extreme cases, where each sprocket has one more tooth than the last, this gives a really smooth riding experience. But the flip-side, of course, is that you have only a small range of gears. If you are riding in varied terrain, this can be a problem.
Cassettes with sprockets as large as e.g. 28 are actually quite a recent thing (for road bikes), as technology has improved. These improve the range of the cassette significantly, making climbing easier, for example. The downside is that sometimes there is a 2 or 3 tooth difference between adjacent sockets, and the "changing" experience is not so smooth.
Again in terms of the range of gears, having larger sprockets at the back can also have advantages at the front - for example you may be able to get away with a double chainset whereas a few years ago, you'd have bought a triple.
So essentially, having a large sprocket (28, say) will give you flexibility when climbing. Having a small sprocket (11, say) will give you an advantage when travelling on the flat at speed (sprinting, if you like). Whereas a cassette with a small range will give you a smoother experience when actually changing. How much smoother is open to question, however.
In terms of what cassette a beginner should use, I would say it is dependent on how strong a cyclist you are. If you are less strong, and will be climbing, then it is almost a no-brainer to go for a large-range cassette. Similarly if you're a strong rider, going to ride flat time trials, then it probably makes sense to get a small-range cassette. And unless you are a good, seasoned cyclist, it is unlikely that you will see any advantage of an 11T ring over a 12T ring - frankly you do a very small amount of riding in top gear.
One last point to explicitly address your mention of weather. As far as cassettes go, weather is irrelevant. You'd do other things related to weather (for example drop your tyre pressure in the rain) but you wouldn't change cassette.
