You don't "have" to. But if you're flying in/out of the US, the TSA may break your suitcase open to inspect the contents if you send it through locked. And you won't get any compensation for any damages.
Yes, this is for security reasons. You should lock your luggage especially if it contains important documents or expensive stuff like your laptop or other gadgets to prevent others from stealing them.
Yes, HOWEVER- if it is locked, and TSA needs to inspect the inside of the luggage, they CAN break it open. You should leave it unlocked.
Yes alcohol in checked luggage is permisible.
If its in your checked luggage, not your carry ons.
Yes, checked luggage is X-rayed and may be subject to further screening.
Yes, wine maybe carried in checked luggage.
Yes, you can pack knives in your checked luggage.
Sure, you can put tools in checked luggage, or at least most tools. If an oxyacetylene torch is considered to be a tool, that would not be a good item to put in your checked luggage, since there is some potential for explosion.
Checked luggage is that which has been checked in: weighed, labelled, and taken away to be loaded onto the plane. You don't see it again until you have landed at the other end and the plane is unloaded. Hand luggage is that which you can take onto the plane with you and have access to during the flight.
yes
Generally, weapons are not allowed in carry-on luggage but can be placed in checked luggage it they are unloaded and properly stored.
No, usually the checked weight is different from the weight of the hand luggage. Check with your airline
Yes.