`RewindBlockIndex` was made to allow nodes upgrading to new consensus rules post-segwit fork to 
download new consensus data (i.e witnesses) without having to go through a whole IBD. It has been pointed than now really few pre-segwit nodes care to upgrade and that this logic may be irrelevant.

See https://github.com/bitcoin/bitcoin/pull/17737#discussion_r358514335 in review  of #17737 for more context pointers.
if (args.IsArgSet("-dustrelayfee")) {
        CAmount n = 0;
        if (!ParseMoney(args.GetArg("-dustrelayfee", ""), n))
            return InitError(AmountErrMsg("dustrelayfee", args.GetArg("-dustrelayfee", "")));
        dustRelayFee = CFeeRate(n);
    }
    fRequireStandard = !args.GetBoolArg("-acceptnonstdtxn", !chainparams.RequireStandard());
    if (!chainparams.IsTestChain() && !fRequireStandard) {
        return InitError(strprintf(Untranslated("acceptnonstdtxn is not currently supported for %s chain"), chainparams.NetworkIDString()));
    }
    nBytesPerSigOp = args.GetArg("-bytespersigop", nBytesPerSigOp);
    if (!g_wallet_init_interface.ParameterInteraction()) return false;
    fIsBareMultisigStd = args.GetBoolArg("-permitbaremultisig", DEFAULT_PERMIT_BAREMULTISIG);
    fAcceptDatacarrier = args.GetBoolArg("-datacarrier", DEFAULT_ACCEPT_DATACARRIER);
    nMaxDatacarrierBytes = args.GetArg("-datacarriersize", nMaxDatacarrierBytes);
    
    SetMockTime(args.GetArg("-mocktime", 0)); 
    if (args.GetBoolArg("-peerbloomfilters", DEFAULT_PEERBLOOMFILTERS))
        nLocalServices = ServiceFlags(nLocalServices | NODE_BLOOM);
    if (args.GetArg("-rpcserialversion", DEFAULT_RPC_SERIALIZE_VERSION) < 0)
        return InitError(Untranslated("rpcserialversion must be non-negative."));
    if (args.GetArg("-rpcserialversion", DEFAULT_RPC_SERIALIZE_VERSION) > 1)
        return InitError(Untranslated("Unknown rpcserialversion requested."));
    nMaxTipAge = args.GetArg("-maxtipage", DEFAULT_MAX_TIP_AGE);
    if (args.IsArgSet("-proxy") && args.GetArg("-proxy", "").empty()) {
        return InitError(_("No proxy server specified. Use -proxy=<ip> or -proxy=<ip:port>."));
    }
    return true;
}
static bool LockDataDirectory(bool probeOnly)