It seems to me that RStudio 1.2.1335 for MacOS uses too much CPU for simple GUI interactions that should not be that demanding, e.g. scrolling. When scrolling through my RScript, the RStudio process often uses 60% of CPU and the QtWebEngineProcess 100%. I noticed because fans often started spinning audibly when I was scrolling through scripts. I tried forcing the OpenGL option in the settings, as well as unchecking the Use GPU blacklist and driver workarounds options. I did not notice much difference. Using the default Textmate theme. It happens even with empty global environment and no packages loaded, and with relatively short scripts (less than 100 rows).
MacBook Pro (Retina, 13-inch, Mid 2014)
2,6 GHz Intel Core i5
8 GB 1600 MHz DDR3
Intel Iris 1536 MB