Atomos Monitor-Recorders provide the benefit of bypassing internal compression that is imposed by the majority of DLSRs and video cameras. The majority of internal recording codecs are based on MPEG compression technology that utilise a heavy compression at up to 50:1 ratio.  Whilst this can deliver files that are smaller in size, MPEG compression is designed as a final delivery codec that is  far from ideal for editing. Similarly, camera manufacturer codecs such as AVC-HD & XAVC L utilise a compression called Group Of Pictures or G.O.P.  This form of compression records only a selected number of full I frames and apply compression by recording the changes in next frame to create a predictive frame.  This is where information in your recording is already lost and as a result your editing system has to use an increased about of compute power to calculate this missing information. So whilst the file is smaller this is due to a reduced amount of information.

Apple ProRes and Avid DNxHD are full I frame codecs that have been designed with editing in mind and as such record each frame as an individual frame to maintain all the image information in a frame using a visually lossless 6:1 compression.  This is much closer to how film captures images and the result allows for a cut to be easily made with out the compute over head on your editing system.