I think you are right on the nail here. For example, if you apply a particular trading method to various timeframes it will give different optimum levels for targets and stops. When one analyses and arrives at an understanding of the appropriate levels for one’s own Trading style then there is no need for advice such as “let your winners run”.
I include in my journalling two additional columns: one for the [I]theoretical [/I]maximum profit the method [I]could [/I]have obtained from the particular trade and the other for how far the price reversed against my trade (whether it was stopped out or not). Over time this gives me data to determine what is the optimal profit level to look for and its percentage likelihood of being achieved - and the most sensible distance to place a stop to avoid accidents as well as unnecessarily excessive loss. It also indicates when there is a change in the overall volatility of the market and a need to tweak the limit/stop levels accordingly. I do this analysis for every trade opportunity in the sessions I watch even if I have not actually taken it.
In the same way as " let your winners run" becomes unnecessary, so your own risk and money management criteria also remove any relevance from another similar phrase: “it is never wrong to take a profit”.
However, unless one is runnng a totally mechanical system, one should never override pure commonsense on those occasions when an action is clearly correct and obvious!