So, what solution would be better for that? In the end it seems that other solutions provide a similar set of features. E.g. Syncthing.
But what's the downside with Git-annex over Syncthing or other solutions?
As I said, handling immutable data (incremental) is easy. You just copy and sync. Kinda trival. The problem I had personaly was all the importand docs (and similar) files I work on. First, I wanted snapshots and history, in case of some mistake or failure. Data checksuming, because they are importand. Also, full peer2peer syncing because I have desktop, servers, VMs, laptop, so I want to sync data around. And because I really like GIT, great tool for VCS, I wanted something similar but for generic binary data. Hence I interested in DVFS system. First I wanted full blown mountable DVFS system, but that is complicated and much harder to make it portable.. Repository aproach is easy to implement and is portable (Cygwin, Linux, UNIX, Posix). Works like a charm.
As for downside, If you think git-annex will work for you, just use it :) For me, it was far too complicated (too much moving parts) even for my DVFS usecase. For immutable data is absolutly overkill, to keep 100s of GBs of data there. I just sync :)