Why is the global minimum tax necessary?

Why is the global minimum tax necessary?
How is it going to affect multinational corporations in the long-run?
Why do tech companies play a role of specific importance in the discussion of tax avoidance and profit shifting?
How will this affect the economy in countries which are considered tax havens?
How will poor countries be affected by a higher corporate tax rate imposed on them?
What impact are we going to see on the consumer end of products provided by tech giants?
Is the profit margin at which the G7 agreement becomes effective too low, leaving a loophole for countries?