Direct Play Question

My question is simple: I have Windows 10 and I am curious what happens when you check that box to enable Direct Play? Does it download a bunch of stuff and more importantly, does it ask you to reboot your computer? I have heard that it doesn't ask you to reboot and that a reboot isn't needed? I'm just curious what to expect once i turn that on. I read a thread on the Steam forums where someone had to reformat after checking that off at some point due to issues/conflicts etc. So I was wondering.....

Thanks.

You mean legacy DP? It does not download anything. Shouldn't unless the OS installation wasn't full for some reason. It's a feature disabled by default, but you can turn it on if needed.

I don't remember if it asks you for reboot automatically, but it's among windows features and you should restart the machine after enabling/disabling any of those.

Dunno about Steam forums either. Due to it's API direct nature, the feature activation can be blocked by antivirus or can get deadlocked by certain applications running in the background. Before turning it on, you should disable antivirus and unnecessary applications (for example Razer audio whatnot, Skype, Teamspeak, and such stuff if you have that) in tray bar.
But after DP activation and machine restart, there should be no conflicts.

DirectPlay is an abstraction allowing developers to add network support with less effort. However, MS decided to remove it when Vista came along. Games that relies on DP did no longer work on platforms later than XP. Enabling it should be harmless as all it does is catch DP calls and translate them to supported API calls.
Just curious but why are you concerned about rebooting your machine?