What is the difference between leaded and lead-free soldering iron tips?

What is the difference between leaded and lead-free soldering iron tips?
First of all: from the environmental point of view to understand, leaded is not environmentally friendly, lead-free environmental protection.
The so-called lead-free, not a little lead are not, but control in the environmental standards allow the scope.
Secondly: from the use of understanding: lead-free soldering iron suitable for high-temperature soldering operations, leaded soldering iron head high-temperature soldering is easy to perforate the hole.