I have a folder A with subfolder CACHE. CACHE contains millions of small files (a cache of some web mapping service) with a total size of 10 GB.
I synchronize folder A between two devices. Syncthing never finishes hashing folder CACHE, but if I add it to ignore list, everything is ok. So it is acceptable for me because I do not need CACHE to by synced.
BtSync hashes folder CACHE very well, but it takets 150 Mb of sytem memory which is unacceptable for me. Adding CACHE to ignores in BtSync does not reduce memory usage. But in Syncthing adding folder to ignores reduces memory usage dramatically, which is very good.