I have followed quite a few RF MCU based designs from Texas Instruments like CC3200, CC2650 etc and in all of them I did not have to worry about the trace impedance between the MCU pins and the antenna.
Their application notes mentioned that as long as the antenna is not far away from the MCU, there is no need to bother with impedance matching.
However now I am designing a RF (2.4GHz) based MCU from NXP, MKW21 to be precise. If you look at the hardware design guidelines, they mention that the trace impedance should be 50 Ω (page 6ff). Here is the pdf link .
Now, my design is space constrained, so the antenna will be kept as close as possible to the MCU. In this case do I still need to monitor the impedance of the track between the tuning circuit and the antenna ?