Should I transcode h264 to ProRes before editing?

I'm starting to edit a project that consist on a dozen of MP4-H264 files coming from two Canon 5Dmk4.

Before starting editing and color correcting, I am planning to transcode those H264 files to ProRes422.
To evaluate the need and benefits of it, I've run my own tests transcoding the source H264 clips with the app 5DtoRGB, I see no diference at the end between transcoding to ProRes422, ProRes422HQ, or simply drop the source MP4 files on DVR and start editing without previous transcoding. Resolve handles well the files and the delivered video seems the same with both methods.

Do you consider transcoding H264 from camera is still necesary on Resolve 15?

The target of the material is 1080p streaming videos for websites, far to be the big screen.

What are the reasons why I should trasncode H264 files to ProRes or similar codecs before starting editing on Resolve?

As far as I understand MP4's are not RAW to begin with they are compressed delivery format files. So I dont see how you would benefit by transcoding MP4 to ProRes.

May be someone else more experienced than me can throw in more light on this issue.

If you are happy with performance and experience which you get while editing your h264 file then conversion is pointless.

What are the reasons why I should trasncode H264 files to ProRes or similar codecs before starting editing on Resolve?

The only reason you should ever transcode or use proxies, is because your NLE won't read/process the source as is, or your machine doesn't have the grunt to process the source as is.

if you're happy with the timeline performance of the h264 media, then go ahead. I'd just make sure to test more than just simple playback-- if you foresee using anything that's effectively a composite (lower thirds, split screens, even cross dissolves), test those too to make sure you're not hitting a performance limit there.

Your exports will take longer coming from h264 sources as well, so if it's the sort of project that requires you to frequently send off drafts for feedback, you might save some time in the long run by transcoding up front.

What are the reasons why I should trasncode H264 files to ProRes or similar codecs before starting editing on Resolve?

Even if you find a performance related reason to transcode, you needn't do it outside Resolve. Try the Optimized Media workflow.