There are a fair number of older TBN threads discussing these buckets in comparison to regular buckets and grapples. Google search does a better job bringing them up than the TBN search function.
Landscaping is probably the job that the 4in1 bucket is most useful for.
Picking up a pile of materials you can get the last handful of gravel or mulch in the bucket, with the right technique combining the curl/dump functions with the clamshell functions. Versus pushing it around with a regular bucket and then shoveling it in by hand.
Another function is grading, whether backdragging or going forward. It is hard to describe in words but the 4in1 has much more versatility and effectiveness on dirt moving/smoothing, compared to a regular bucket. You can use either the clamshell or the short bucket, going forward or back. And the extra weight is a help here. You can do a better job faster. It can also be used to doze up dirt pretty well, at least with a strongly built industrial style backhoe.
For clearing bushes and small stumps you can chomp down on them and pull up, easy peasey. Similarly for grabbing debris or small logs and branches.
For building a pile of rubble or trash, or loading same into a dump trailer, the 4in1 can be used as a bottom dump rather than tilt-dumping a regular bucket, this gets you an extra amount of height that is very useful.
The only thing I use the regular bucket for is - because it holds more - moving material and distributing it. I also have a grapple, that is much better at brush and roots.
I guess I would say that the 4in1 is like a swiss army knife compared to a bowie knife. Does quite a number of things pretty well that the straight knife cannot do.