For most programming languages, you get out-of-the-box syntax highlighting. Packages like ESS and Elpy provide additional features like autocompletion, documentation and debugging capabilities. The number of IDE features available will vary by language, but at minimum there is probably syntax highlighting and some form of autocompletion.
Figure 1: "Autocompletion"
One of the things that I enjoy is easy access to help and function parameters … which often also come with autocomplete.
Figure 2: "Help for Functions"
Figure 3: "Parameter help for Function"
Enough with the print statements already and debug that R and python code!
Figure 4: "Interactive debugging with conditional breakpoint"