When should I use pcall?

Use PCalls to handle things that could possibly error, such as datastores or Http requests, or if you're finding code doesn't work, you could do something like:

local success, err = ypcall(function()
    ppppppppppprint("i error!")
end)
if not success then
    print("Oops! I errored: " .. err)
else
    print("I succeeded!")
end

This is a good tool for code errors, it is a good ally of a function if you want to keep track of what went wrong, you can use pcalls to keep track of your code carefully, putting one at each important step.