I use FamilySearch.org far more than I use any other source for data. They maintain a huge database of indexed records that can be accessed and searched FREE of charge. You don't even have to set up an account with them to search their records, you can remain anonymous. There is no need to put your family tree on their site, and they will fully cite the record you are looking at, including the link, that you can use as a source on WikiTree, which allows the person who is looking at the profile on WikiTree to click on the link and see the source material without having to have an account or login to FamilySearch.org.
In return for this, I volunteer there, and have indexed and arbitrated many, many censuses. birth, marriage and death records, obituaries, and passenger lists, to name just a few types. All of the records are indexed by at least two separate people, and then the discrepencies are reviewed by an individual functioning as an arbitrator. This ensures more accurate records.
I volunteer at FamilySearch.org as a payback for all those online resources that they make available for free to all us genealogists, and no, I am not a member of their church.
I don't know the site's policies regarding reposting copies of original source documents, but as they will create the citation and link, it is unnecessary to add the original source documents to WikiTree.