Should you shoot flat when shooting with a DSLR?
There are two schools of thought on this topic but nothing I know has suggested that shooting with a flat profile is a bad thing. Here is what I understand:

1) When shooting with Canon DSLRs, it's generally advised that you shoot with a flat profile (Technicolor cinestyle, Prolost, etc.) and over expose (but don't clip!!) and you get a picture with much more detail, specifically in the shadows. Here is a video showing this: https://vimeo.com/73909925

It's rather long, but the entire series is good. In there he specifically shows the effects of shooting standard and exposing correctly v.s. shooting flat and over exposing. Lots of detail in the shadow is preserved when performing the latter. 

2) A lot of more professional film makers (Shane Hurlbut, and Stillmotion) suggest that you should use a color profile that best matches your final color result. Less work is needed in post, and  you have a better feel for your film. I think I see this school of thought from professionals more often because the gear they own has high dynamic range and retains so much information anyways, so detail isn't something to worry about. 

Personally, I'm not a professional and I record with a Canon 550D but I use the Standard Profile when exposing my shot (aka, over exposing) and switch to technicolor cinestyle when I hit record to give me more color grading flexibility in post.