Hello @arkiboys
Even I see in many cases a separate repository is created for ADF, I think this is for a better collaboration if multiple teams are working on different Azure components
If in your case the above condition applies, then you can create a separate ADF repository
If the team is small and less collaboration is needed, like in one of the projects I did, we extracted the ARM Template from ADF and checked-in to a folder named ADF in a single repository where other Azure components are checked-in
In this case, we were independent to keep few items till development environment only, when we export the ARM template we manually remove the items we don't want to deploy, I know this is tedious but we felt this a better approach than publishing all dev items into repository