I have tested morewrites and scrwfile in my template which uses so many writes that without loading any of those packages I would run into the no room for new \write problem.
I find that with scrwfile I can use more packages that use an output. In my case these are
- TikZ and pgf (without external)
imakeidxglossariesfancyvrblistingstitletoctodonotes(?)
There may be more, but these are the ones that I know of which use \write
Technically I wonder If anyone can describe what are the differences between these packages and if there is a way to count the free \write outputs.