Speaking of Debian: don't misunderstand, Debian is one of the greatest Linux distributions ever! So is the community. But if you are used to everything working out-of-the-box for such a long time, and you have a good dozen computers to look after, then the hours of setting up basic functions after the fact can be very tedious.
Even if you use RHEL there is still configuration that needs doing, system updates need applying, etc.. Ansible, Chef & Puppet exist to automate and simplify this process.
IMO Ansible is the best simply because it doesn't try to build clever plans. You outline what actions you want to perform, files to copy and dependencies to run first and it will quietly run each sequentially.