what does link mean in truffle?

Question

I saw the following : what does `deploy.link` exactly do in `truffle`

I have safe.sol

library safe {
function safeMultiply(uint256 a, uint256 b) internal pure returns (uint256) {
    if (a == 0) {
        return 0;
    } else {
        uint256 c = a * b;
        assert(c / a == b);
        return c;
    }
}



}

In my contract, I have this:

import "../libraries/safe.sol";
contract TokenSale {
function test() public view returns (uint256){
    return safe.safeMultiply(5, 10);

}


}

Now, when deploying contract, I just have deployer.deploy(myContract) , It deploys the contract successfully and , test function works as expected. There was no need to use deployer.link from truffle.

So , why does the stackoverflow question above I linked or even truffle's website explain like this that deployer.link is needed to make this work ?