So I'm bit of an old school guy. I've got a desktop and a laptop running Windows 7, and on the laptop I've also got a virtual machine running Windows XP, which I use occasionally to play Simcity 4 (a city buliding game), as well as other old games that won't run on Windows 7. I also use it for casual internet browsing and doing college work.
In some ways, I prefer using it to my host machine because it's nice and quick with no distractions and no slowdowns (as on my host machine I have a lot of tabs and other programs open which slows things down to a crawl usually).
I also love the simplicity of Windows XP and love the way it looks with it's bliss background (remember the green hill anyone) which reminds me and my mum of tellytubby land (anyone remember watching that as a youngster?).
Also the green start menu, blue task bar, good looking icons and the user-friendly interface.
Also it's sooooooooo much faster than my host machine even though I'm only running XP on 512MB of RAM, whereas my host machine has got 3GB of RAM but about three times as slow lol.
WIndows XP runs really smoothly on just 1/2 GB RAM with not many background applications installed. Try running Windows 7 or (god forbid) Windows 10 on 1/2 GB RAM and see if you get the same results (spolier: you will not!).
Another reason I use it is for nostalgia reasons. I used Windows XP from Year 4 in Primary School until Year 10 in high school (when my school sadly upgraded to Windows 7). I also used it as my host machine from 2009 - 2014. The startup sound, the Please Wait, Windows is starting up, preparing network connections, applying computer settings, loading your personal settings etc messages at bootup and logon and shutdown.
I also use Microsoft Office 2003 on my Windows XP VM to do my college work on. It is still one of the best versions of Office in my opinion as it is simple and easy to use and was the last version to use pull-down menus before they brought in the ribbon interface in Office 2007.
I also love the areo interface on WIndows 7 as well, and both WIndows XP and Windows 7 are both superior to Windows 10 in my opinion.