[andwaal]

Lets do an example. In many of the enterprise applications I work on large datagrids are used. I did a loot of research in order to find the best open alternative, from what I found this seems to be http://datatables.net/ . It seems like a great product with a lots of features, plugins and ways to tweak it. But still KendoUI`s got features like proper grouping, binding to remote data(filtering, sorting, grouping etc), advanced filtering, fast customisation of headers/rows/cells, proper select/multi-select and so on. Im aware that you could probably do all these things with Datatables, but still you would have to find the appropriate plugins, browse through bad documentations and properly end up implementing half of the missing features your self. Of course this could be done, but with KendoUI you got it all out of the box, with proper documentation. And if you don`t figure it out, you got professional support with fast response(great for junior dev). Yes KendoUi got a steep licence cost, but it don`t take long to realize that it`s worth it. I could to exactly the same example for the TreeView component(and to some degree the Data Visualization package, though the open alternatives seems much more competitive, if not better, here).

So to answer your question, from my experience using KendoUI reduces the time needed for the average developer to complete the task.