Xfce is a very light desktop, though to be honest, MATE uses hardly no more resources & loaded with much more software, requires no more space. Also very little difference in ISO size.
The only reason why I'd see that one would want Xfce over Cinnamon (or MATE, which is a closer comparison), is to have a minimal desktop, just what's needed, and no more. One can add packages as needed/desired. And Xfce boots very fast, even on low spec hardware, such as the many dual core Pentiums & Celerons that shipped with Windows 7. On these, the system will run better than new, because these are no longer weighed down with garbage that should mandate a quad core i7 be installed.
These are the majority of the folks I've managed to get to make the Linux leap, those with computers built between 2009 & 2011 (many 1st gen 'i' series CPU's in there). The install of Mint Xfce or MATE (performance wise) would be the equivalent of upgrading from one of these low spec CPU's to say an i7-626/640M & keeping what they have. Of course, I don't mind performing upgrades, that's part of my upgrade cash, yet I don't see the need to spend $40 for a CPU from a reliable source, especially after my labor is figured in ($125 total), on a notebook that they may never get that much for if sold. I advise them to purchase a low cost SSD (if affordable), and at no cost, will perform most any Linux install.
I'll carry 4 different flavors of Linux with me, LM Xfce, MATE & Cinnamon, and Ubuntu 16.04 for those who likes the modern UI. Most goes with Xfce or MATE.
On the other hand, I've read more articles than I can count on how Linux Mint Cinnamon is the drop in fit for Windows 7 users, because it has very nice themes, that 'Aero' or glassy look w/out using too many resources, and overall is rapidly becoming Linux Mint's #1 distro. And I expect more to make the leap as EOL for W7 nears.
So it's a matter of personal preference, having a very attractive desktop (as you know) or a minimal one to build upon. Cinnamon can be added to much any distro, though have never tried with Xfce, on the other hand, unless one has nothing except time on their hands, experiment away & see which is the best.
I really don't believe that Xfce gets the credit it deserves though, and one reason why I carry it with me for a demo when one wants to try Linux on their computer. It's always, unless a specific one is already chosen, the first one that I test out, mainly to get a feel of their hardware for myself to see which others are a waste of time to fool with. Still, my best success is with MATE, followed by Xfce, and Cinnamon. Have installed less than 5 Ubuntu OS's for others since Unity became baked in, before then, was installing a few of these, which was my first taste of Linux. Back in the days when Canonical shipped the CD's for free.