purpose of ~/.emacs.d/auto-save-list/

Question

A directory titled auto-save-list appeared in my .emacs.d folder. In my init.el file, I did not explicitly mention I want this folder to be made. What is the purpose of this folder? I noticed it seems to always be empty: files being auto-saved (starting with #) appear wherever the original file being edited is, not in the auto-save-list directory.

Answer 1

If you search the manual or its index for auto-save-list you will find:

Emacs records information about interrupted sessions in files named ‘.saves-PID-HOSTNAME’ in the directory ‘~/.emacs.d/auto-save-list/’. This directory is determined by the variable ‘auto-save-list-file-prefix’. If you set ‘auto-save-list-file-prefix’ to ‘nil’, sessions are not recorded for recovery.

 – C-hig (emacs)Recover RET

I did not explicitly mention I want this folder to be made.

Emacs and elisp libraries in general write to ~/.emacs.d/ when they need to save data. That's one of the purposes of this directory -- to provide a common place for such files to be written to; and this typically happens without asking explicit permission (although it's also pretty common for you to be able to customize the filename in question if you so wish).

Answer 2

phils already answered the specific question, but to answer the more general question of what to do about miscellaneous files automatically created by Emacs, check out the no-littering package.

Auto save files (the ones with '#') are not handled by no-littering, but the readme gives a work around for those if you wish.