I think the problem with just using append to file is that it won't preserve the shape of the file. For example, if I had a file with
* Notes
** Note 1
blah blah
** Note 2 blah blah
* Tasks
** DONE task 1
** TODO Task 2
and I decide to archive note 1 and task 1, I would like them to both appear under the same headings and with the same level. If the process just uses append to file, I can have this for the first archiving i.e.
* Noes
** Note 1
* Tasks
** DONE task 1
but then later, I decide to archive note 2, if append file is used, I will end up with
* Notes
** Note 1
* Taks
** DONE task 1
* Notes
** Note 2
which is not what I want. I want
* Notes
** Note 1
** Note 2
* Tasks
** DONE Task 1
So, if we want to preserve hierarchies in our archive files and not have everything jumbled up together, the system has to parse the file. If you are also using something like Categories, then even more work needs to be odne to update the category lists.
What I tend to do is mark items with the ARCHIVE tag and leave them in the file and then every few months, move archived data to archive files. It can still get slow, but I don't do it often, so it isn't too much of a hassle.