A bit late to the party, but I just tried #12653 and noticed some non-intuitive behavior (on macOS), that's probably worth explaining release notes and help.

Before this new feature I kept the entire datadir on an SSD drive, so I launch with: `bitcoind -datadir=/Volumes/SSD/Bitcoin`.

Initially I naively moved `/Volumes/SSD/Bitcoin/blocks` to `/Users/bitcoin/blocks` and added a line to `/Volumes/SSD/Bitcoin/bitcoin.conf`: `blocksdir=/Users/bitcoin/blocks`.

I then realized that I shouldn't have moved the `index` subdirectory, so I moved that back to `/Volumes/SSD/Bitcoin/blocks/index`. Having an empty `blocks` dir with just and `index` subdir is a bit weird. Perhaps after @jimpo's #11857 is merged, we could just move / assume all indexes to be there (if `-blocksdir` is set)?

Worse, it created a directory `/Users/bitcoin/blocks/blocks`, which seems like a bug. I had to set `blocksdir=/Users/bitcoin` instead.
else if (it->path().filename().string().substr(0,3) == "rev")
                remove(it->path());
        }
    }
    
    
    
    
    int nContigCounter = 0;
    for (const std::pair<const std::string, fs::path>& item : mapBlockFiles) {
        if (atoi(item.first) == nContigCounter) {
            nContigCounter++;
            continue;
        }
        remove(item.second);
    }
}
static void ThreadImport(std::vector<fs::path> vImportFiles)
{
    const CChainParams& chainparams = Params();
    RenameThread("bitcoin-loadblk");
    ScheduleBatchPriority();
    {
    CImportingNow imp;
    
    if (fReindex) {
        int nFile = 0;
        while (true) {
            CDiskBlockPos pos(nFile, 0);
            if (!fs::exists(GetBlockPosFilename(pos, "blk")))