Have to declare an interest here, I've had an 80mm scope for a few years) so my opinion could well be coloured by my experience
Their reach. For distant animals (say birds on mud flats/at sea/across lakes or distant mammals) they give a much better view than binoculars. A view that at times will allow certain identification which would not be possible with binoculars.
Another but more minor one. Depending on the size of the objective and the magnification scopes can produce as bright an image as lower powered binoculars. For example a pair of 10x40 binoculars have an exit pupil of 4mm, which is the same as an 80 mm scope used at a magnification of 20, so an image of the same brightness but with twice the magnification. This example is the ideal and the construction of the scope(and the binoculars) can affect the brightness of the image. In addition, unless the viewing conditions are poor (very cloudy or getting toward night) the size of the exit pupil is not that important.
They need some sort of support. This might, for smaller scopes, be just resting on a convenient support but I think most need a tripod or at least a monopod.
Small one are fairly easily transportable but larger ones are not light or small and the larger ones definitely need a tripod.
Carrying them around might be a problem. I've carried my scope attached to a tripod around Dungeness with no problem, but it was really pleasant warm day in June. It might have been different on a rainy blustery day. There are a number of rucksack style carriers for scopes and their attached tripods which should make things easier but again add to the bulk and cost.
They are not as easy as binoculars to rapidly point and focus towards a bird or other animal.
However, for long range views they are excellent.
Although I have had my scope for a while I haven't used it as much as I thought I would and while not having access to the scope would be a slight inconvenience, I definitely would not like to be without my binoculars.