I think of the +tlrc as part of the filename extension--AFNI calls it the view. It specifies what the spatial coordinate grid "means" semantically. AFNI tries to make it difficult to accidentally mix data that are incompatible.
"+tlrc" tells AFNI that the spatial coordinates of the dataset are Talairach space. Other options are +orig for "original space" and +acpc for "AC-PC-aligned space".