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.
if (gArgs.GetBoolArg("-upnp", DEFAULT_UPNP)) {
        StartMapPort();
    }
    CConnman::Options connOptions;
    connOptions.nLocalServices = nLocalServices;
    connOptions.nMaxConnections = nMaxConnections;
    connOptions.nMaxOutbound = std::min(MAX_OUTBOUND_CONNECTIONS, connOptions.nMaxConnections);
    connOptions.nMaxAddnode = MAX_ADDNODE_CONNECTIONS;
    connOptions.nMaxFeeler = 1;
    connOptions.nBestHeight = chain_active_height;
    connOptions.uiInterface = &uiInterface;
    connOptions.m_msgproc = peerLogic.get();
    connOptions.nSendBufferMaxSize = 1000*gArgs.GetArg("-maxsendbuffer", DEFAULT_MAXSENDBUFFER);
    connOptions.nReceiveFloodSize = 1000*gArgs.GetArg("-maxreceivebuffer", DEFAULT_MAXRECEIVEBUFFER);
    connOptions.m_added_nodes = gArgs.GetArgs("-addnode");
    connOptions.nMaxOutboundTimeframe = nMaxOutboundTimeframe;
    connOptions.nMaxOutboundLimit = nMaxOutboundLimit;
    for (const std::string& strBind : gArgs.GetArgs("-bind")) {
        CService addrBind;
        if (!Lookup(strBind.c_str(), addrBind, GetListenPort(), false)) {
            return InitError(ResolveErrMsg("bind", strBind));
        }
        connOptions.vBinds.push_back(addrBind);
    }
    for (const std::string& strBind : gArgs.GetArgs("-whitebind")) {
        CService addrBind;
        if (!Lookup(strBind.c_str(), addrBind, 0, false)) {
            return InitError(ResolveErrMsg("whitebind", strBind));
        }
        if (addrBind.GetPort() == 0) {