All types of flags are combined to achieve the best performance and lowest ping/latency in Roblox.
To apply these flags, open Bloxstrap, go to Engine Settings, scroll down, click on Fast Flag Editor, click Add New, then click Import JSON. Copy everything from flags.json, paste it into the input box, click OK, and launch Roblox.
Warning
I've noticed that people are getting banned for using fast flags, not just these specific ones but any type of fast flags in general. So if your account was banned for something like 'modified Roblox client,' I recommend not using any type of flags. I'm using them myself and haven't received any warning or a ban from Roblox, but still, use them at your own risk.