local pointers of functions

[Jarod24]

So i've been looking though the blizzard files and i have come across stuff like this:

--this is from GameTime.lua

local date = date;
local format = format;
local GetCVarBool = GetCVarBool;
local CalendarGetDate = CalendarGetDate;
local max = max;
local tonumber = tonumber;

Does such re-declaring of global functions as "local" like this improve performance?

Its late and i'm sorry if this has been answered a thousand times before.