Pre Comp vs. Pre Render , what do you use?

There is no single answer to your question, as all jobs are different. But here are some thoughts.

Retaining a Precomp gives you easy flexibility to make changes within the Precomp.  If things are likely to change, it may be easier to keep it that way.  

If your Precomp content is complex, or contains many layers, it probably takes a fair while to render.  Pre-rendering the content will almost certainly improve your preview render times while you work.  I recently worked on some complicated comps with a sports stadium background.  Because of Covid we couldn't shoot extras in a stadium, so I shot a few individuals on green screen and comped them into the empty stadium seats.  The finished comp had 300 video layers of keyed sports fans. It took about 45 minutes to render 5 seconds of content, so it was hugely beneficial for me to pre-render it.  That way I could work on the foreground components and preview quite quickly.

If your Precomp is not particularly complex, or doesn't contain many layers, it may not add much efficiency to pre-render it.  

Hard drive speed is quite important if you're rendering content with many layers of video footage.  If you have slow hard drives and a complex project with many video layers, the hard drive may slow you down.  This can make pre-rendering beneficial: its better to be reading one video file instead of 20.  But if your precomp is all graphic elements and doesn't constantly use the hard drive, pre-rendering to a slow hard drive may slow your previews down.