I still have 2 desktops running XP and my Laptop (the one I use now) that's still running Vista.
And yes, there are some minor disadvantages too, such as Microsoft no longer supports XP and Vista so no updates, (that may translate into a plus for some of you Win10 users who hate frequent updates from Microsoft that sometimes crash your system)...And most Browsers and A/V software companies have stopped updating the engines of those programs but still release updates for definitions for those programs so still OK and they work fine...
As examples, I had not run MalwareBytes nor SuperAntiSpyware for about two years..Yesterday I let them update with the latest definitions and ran both while booted into Safe-Mode....not one finding!!! In the distant past they would always find problems to fix, but nothing now..
One logical reason why XP and Vista systems are now more secure than they were in their hayday...Hackers and malware writers no longer attack these systems...they're too busy developing bad stuff that attacks Win-8 and Win-10 systems..so they ignore the few systems that are still running XP and Vista..
I may still upgrade my laptop with newer hardware and operating system one day but for right now I'm very pleased with the way these computers continue to perform and I can do everything on the net that I've always done..