Pokahontas, because I know damage happens whether I like it or not, and particularly because my strands are fine and so will not be able to hang around the way your coarser strands might, I do not wait till I see the splits. If I did, my hair would be breaking something awful and I'd be stuck at SL like I was for 30+ years of my life. So I dust before I can see them thus catching the splits at the microscopic scale and I dust ALL the strands because I know that just because I cannot see them doesn't mean they are not there. I know wear and tear is happening all the time. A nice clean cut slows down the damage and buys me more time to grow some length but it just creates a new end that will slowly start to wear and tear. The idea to keep splits just at the "starting point" where they haven't wrecked much havoc to my hair and by doing so, I don't get to experience the breakage or thinning that occurs if I wait any longer.
By doing this, I find I can afford to get away with dusting a very tiny bit and still have my hair looking full from base to ends and also I'm able to see it gain some length. Doesn't mean I don't have any splits. They are just too small for me to see them (think: at their starting stages) and my fine stands retain better if I keep splits at that small scale.
About shorter strands: I don't worry about those for these reasons:
[*]they are shorter because they haven't been around for long to endure the wear and tearthat older strands found on the longer strands have endured;
[*]shorter strands enjoy "protection" without me needing to PS by virtue of being tucked away inside the longer strands.
My theory is split hair will break off whether you trim it yourself or leave it there, so if you have WL length and your CBL hair has splits, then that is as bad as having mid-shaft splits and there has to be something you're doing wrong to cause your hair to be splitting at such an early stage when the rest of your strands have survived all the years it took to get to WL. Hair that is split WILL break, and if splits are happening to hair that is only a few years old, on a head whose hairs usually survive many more years...then something is wrong. Alternatively, you might just have the sort of coarse strands that can split, tear and continue to hang on and make it to great lengths. And if you have a lot of hair, such damage may not be the kind that affects that look of your hair. If you consider this lady:
Her hair splits too, only she must have some really strong/coarse strands that no matter how much styling, washing, exposure to the elements her strands endure, it's only when her hair is almost as long as she's tall that this wearing of strands leads to breakage or at least tearing off of the splits--and so her hair starts to thin. But even then, you can see that she still has strands that continue to hold on so that she ends up with a skinny tail probably made of many strand but which looks like only 3 because wear and tear has creates skinny end. So splits on her hair may not affect her hair the way they do my fine and oh-so-weak strands. And likewise, the reason YOU can find splits in your long hair is because they don't affect you the way they do me. So you can afford to leave them in your hair for a while. (BTW, how do you S&D? You don't do the twisting method do you?)
Since it's impossible to inspect every strand, it seems as futile to me as counting how many drops it takes to fill an ocean to expect every single strand of your hair to be in perfect shape and to be worrying about the strands that only recently started growing and are therefore are stronger and healthier than the older longer strands that have been around to actually experience damage.