How does the Big Bang Theory affect us?
Well, its the very reason we are here and exist today!
The Big Bang essentially formed the entire universe that we know and all the elements, forces, stars and planets in it.
More specially, most of the hydrogen and helium in the universe today was formed during the early days of the Big Bang. Hydrogen is a key element in the organic chemicals of life. For example, hydrogen helps bond other chemicals to form the DNA that is in nearly every cell in our body!
It doesn't really!
I've been teaching it, and enjoying teaching it, for many years because students find it fascinating, but it is of no practical importance whatsoever.
To paraphrase Sherlock Holmes 'you say we go round the sun. If we went round the moon it would not make a pennyworth of difference to me or to my work.' (taken from https://simontkaye.com/2013/04/19/the-epistemology-of-sherlock-holmes/)
Much of modern knowledge is not useful, but it enriches the student immensely, in my view.