@RomanZ @Helen
I am on a 2010 MacBook Pro, 2.4 GHz C2D, 8GB RAM.
macOS Sierra 10.12.6 on SSD, while 348 GB Sync folder is on separate, internal HDD.
Not only does WindowServer regularly use 20% + CPU while Sync icon is animating, Sync itself pegs my processor at max the entire time it transfers files. Why is transferring files so resource intensive? No other BitTorrent application I have ever used has used that much CPU, even while UL/DL at multiple MB per second. Sync is not necessarily "Indexing" during this time, but when it is, my computer is almost unusable.