I have years of backtests with thousands of trades for multiple strategies, so I have a pretty good idea how they perform in a variety of conditions. I do make adjustments and temporarily stop trading some strategies based on basic market timing, not to improve returns but to reduce risk. I am also aware that markets can change and strategies can stop working so I trade multiple strategies and I monitor them. I am always looking for better ideas so generally I stop trading a strategy because I have a better one to take it's place. In the summer of 2008 all my longer term (weeks) long strategies started breaking down early in the summer. My short term trading was holding up so I switched to this entirely. This was entirely subjective, but it was very uncharacteristic to see everything else breaking down. I was slow to get back in to the longer term strategies, but my shorter term strategies are better anyways, so I was in no hurry.
Momentum strategy = growth stocks in a bull market. Rough measure of bull market = Dow 50DMA > 200DMA and only pulled back 25-30% below last peak (or 52-wk high). Of course this means you could suffer 25-30% loss while still thinking the trend is up. IMHO always be both long and short, or similar, for example long and hedge. When your short/hedge outperforms your long, consider stopping trading or reversing the weighting. Some strategies work better during choppy/nontrending markets. You can look at VIX (volatility index) and see if strategies fare well/poorly during high VIX periods.
I attended a free webinar, which is where I learned about the "JoeKrut diff" methodology (and see above post for my own experiences/verdict on using it). I don't have more information than that ...