[asdff]

Why even break it down? If you are using grep and presumably editors that can go to a pattern anyway you might as well write to a single file.

[herodoturtle]

I also manage my notes on the go by opening the Dropbox app on my phone and editing the txt files from there. Having subfolders helps with navigation on the Dropbox app.

[hiq]

In case of infrequent synchronizations you reduce the number of conflicts by having separate files rather than a single big one.