`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 (m_ibd_chainstate && !m_snapshot_chainstate) {
        LogPrintf("[snapshot] allocating all cache to the IBD chainstate\n");
        
        m_ibd_chainstate->ResizeCoinsCaches(m_total_coinstip_cache, m_total_coinsdb_cache);
    }
    else if (m_snapshot_chainstate && !m_ibd_chainstate) {
        LogPrintf("[snapshot] allocating all cache to the snapshot chainstate\n");
        
        m_snapshot_chainstate->ResizeCoinsCaches(m_total_coinstip_cache, m_total_coinsdb_cache);
    }
    else if (m_ibd_chainstate && m_snapshot_chainstate) {
        
        
        
        if (m_snapshot_chainstate->IsInitialBlockDownload()) {
            m_ibd_chainstate->ResizeCoinsCaches(
                m_total_coinstip_cache * 0.05, m_total_coinsdb_cache * 0.05);
            m_snapshot_chainstate->ResizeCoinsCaches(
                m_total_coinstip_cache * 0.95, m_total_coinsdb_cache * 0.95);
        } else {
            m_snapshot_chainstate->ResizeCoinsCaches(
                m_total_coinstip_cache * 0.05, m_total_coinsdb_cache * 0.05);
            m_ibd_chainstate->ResizeCoinsCaches(
                m_total_coinstip_cache * 0.95, m_total_coinsdb_cache * 0.95);
        }
    }
}