Often at the end of astronomical papers there is written that it was created using the AAS LaTeX macro v5.2 . Do I understand this right that one can download such a template with all preamples at the beginning already set and that one only needs to write the text, insert graphics, tables etc. So you don't have to worry and mess around with the preamble?
I can't speak for the AAS, but I am well acquainted with the templates from AMS (the American Mathematical Society). These templates are quite basic, containing only a few packages that are known to be used almost universally, along with recommendations in the form of comments regarding other packages that are known to be compatible with the document classes.
edit: Templates from the AMS are not the document classes, but outlines that consist, most basically, of three commands:
A template may specify a few packages and recommend a few definitions (for example,
the AMS templates recommend the
graphicx package and provide a "starter set" of
theorem definitions, as well as a number of comments with further recommendations),
but should not include anything that the author has to strip out before use; such
a file is what I would consider an example.
Different authors have different requirements, so loading in many packages that may be useful is not good practice -- it may result in confusing conflicts. With some experience, you will learn what packages and custom commands you usually need. Then you can create your own collection and copy it into the preamble of a new file as a starter set.
When your work on the document is complete, review the contents of the preamble and remove the packages and commands that you haven't used. If you are submitting an article to a publisher, the editors will appreciate it.