When To Render In Place

I have just purchased Cubase Pro 8; I have experience of Cubase in other versions, but am struggling a bit with the Render In Place feature on Cubase 8. I have recorded a song made up so far of 9 VST tracks including EQ and effects where wanted/needed; I’m happy with the mix and now I just need to add vocals. Please can someone help me with when to render the existing vst tracks, how to do so and why it is needed.
Apologies if this sounds a simplistic question, but any help/advice would be really appreciated.

Mostly this is a system-resource issue where you’re taxing your CPU with too many VSTIs, Effects, etc. Rendering those tracks converts everything into audio files (wet or dry with effects per your choosing) which use considerably less CPU resources. You would also want to convert VSTi tracks into audio files if you’re wanting to edit that data via the audio and sample editor to achieve results that you cannot do with MIDI editors. Here’s a nice overview of this: