There are plenty of reasons to use proper citations in your research. Here are just a few:
Historians typically use the Chicago Manual of Style to format their writing, preferring the notes-bibliography style for citations. (The author-date style of citations is used by some in the social sciences.)
When working on larger research projects, especially over an extended period of time, it can be helpful to use a citation management tool. These allow you to store citation information from lots of sources, organize them into folders, add subject tags or research notes to help sort and organize your materials, and even create shared folders for group projects.
I recommend Zotero, a free and open source citation management tool. In addition to helping to keep your research organized, Zotero works with Word, LibreOffice, and Google Docs to automatically generate citations and bibliographies in whatever citation style you need.