I would like to hear more about your system if you feel so inclined. How do you determine the reinvestment triggers?
I've discussed it a few times before, and I'm sure the long-time members are tired of seeing it again! And it is all mechanical in operation, no more timing involved than a triggered rebalance. Also, we are cash flow negative, even with DW working, so excess cash can be spent in a few years without touching equities. Something slightly different along the lines of over-rebalancing might work better than this during accumulation.
Raising cash:
I have a simple x% market return, x% inflation projection for my retirement portfolio. It assumes I sell enough equities each year to support my expenses. So if the portfolio is doing well and exceeds next year's sell point value, I'll sell immediately to lock in that cash for next year at the desired market return. I'll do that for a few years if the market keeps going up. If the market goes down, then I've got cash to live on for a while. My way of smoothing out the returns. All mechanical.
If I don't have any extra cash I sell equites as needed. I have a nominally all equity portfolio and no desire to hold cash or bonds long-term
Reinvesting cash:
If I have more than a year or so of cash, I'm happy to reinvest it if the market goes down more than 20%. I use (SPY + EFA)/2 with dividends reinvested as a market proxy for this number. I divide the cash into 5 equal amounts and reinvest one part each at -20%, -25%, -30%, -35%, and -40%. You never know how low it will go. I added a couple of steps during the last big market drop by adding HELOC money into the mix (now repaid and ready to go again). I was just about to transfer allocations from conservative funds into volatile funds, the last step I could take with no cash to reinvest, when the market finally turned back up. However, I did reserve enough cash for about 12 months of expenses so we could wait for the market to recover.
Even if you have to sell before a full recovery, you are taking out cash that was used to buy equities that were 40% down and have recovered, a net positive. The risk is of course that you sell equities at a 50% discount that you bought for a 40% discount, but that's still not too bad.
Again, absolutely mechanical, though exciting near the trigger points. I also like to work with ETF's when doing this so I can hit the triggers precisely intra-day. The last day of the 2009 drop included a 1% rise or so late in the day, IIRC, and I didn't place the MF buys because of that. And then I never had the chance because the market never reached that low again.
So, it's a way to ensure you sell equities at your targeted yearly prices to meet your retirement goals, even if you sell early sometimes. And a way to reinvest in a bear market sometimes. Otherwise, I just sell equities as needed during a hopefully boring average market. That hasn't happened very often so far.