`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 (!accepted_header)
        return false;
    
    
    
    bool fAlreadyHave = pindex->nStatus & BLOCK_HAVE_DATA;
    bool fHasMoreOrSameWork = (m_chain.Tip() ? pindex->nChainWork >= m_chain.Tip()->nChainWork : true);
    
    
    
    
    
    bool fTooFarAhead = (pindex->nHeight > int(m_chain.Height() + MIN_BLOCKS_TO_KEEP));
    
    
    
    
    
    
    if (fAlreadyHave) return true;
    if (!fRequested) {  
        if (pindex->nTx != 0) return true;    
        if (!fHasMoreOrSameWork) return true; 
        if (fTooFarAhead) return true;        
        
        
        
        
        if (pindex->nChainWork < nMinimumChainWork) return true;
    }