From my perspective the mindset with Debian is that distribution packages are never going to be the super latest, but are going to usually work well.

If I need something bleeding edge it's straightforward to just download the source from wherever and install it myself with stow in /usr/local, which makes it easy to remove/upgrade if needed. I anyways do pretty much everything in VMs, so package availability for my "base" system (which I mostly use only to run VMs) is not that big of a deal. If I need bleeding edge I can always spin up an arch linux VM...

Debian testing hardly breaks anything unless one does a blind dist-upgrade instead of upgrade. The normal "apt-get upgrade" attempts to install the latest software versions unless the process requires the removal of other software (except the older version of course) so that (newer versions bugs aside) it won't break the system. The "apt-get dist-upgrade" will attempt to install the latest version even though it could force the removal of other packages, which can completely bork the system in many ways (missing libraries, etc). When I use it I often do a normal upgrade followed by a dist-upgrade and check all packages it would uninstall before allowing it to proceed, if I do. I've burned myself multiple times before learning this:)

Ironically, the "dist-upgrade" must be explicitly called on the command line, but is the default setting in Synaptic (called "smart upgrade" there). Synaptic is a GUI package manager most newbies would probably use in place of the command line, so I would expect its default settings to be more on the safe side.

Debian stable has never been terribly old for several generations now.

Does what you do with your computer matter? Then you probably want to consider doing it on a stable platform.

Do you want to experiment? Sure thing, have fun — but be aware that you may lose data as a result.

Debian stable has been an excellent platform for me for the better part of a decade. But I'm unafraid to install newer version of some software where appropriate (e.g. emacs, or graphics drivers).

Been running Debian with XFCE on Testing lately. No problems here.