This is for the students and those on welfare, who most people will generally say cannot invite people to Germany. Theoretically, you can still invite someone to Germany BUT the person has to be able to afford their stay here. Examples are students who are inviting their parents to attend their graduations or just coming to “check-up” on them.
For students, maybe the invitation letter won’t change much but for those on welfare the invitation letter can save the invitee the need to provide hotel reservations when applying for the visa in their home country. I assume the student doesn’t have a home large enough to accommodate visitors but if you do, then you can always include that bit of info for the embassy.
The invitee will either have to show bank statements in their home country to prove that they can afford their stay in Germany OR have a fixed bank account in a German bank where they are allowed to withdraw €150-€300 a day during their stay here.