If people don't have the time or inclination (or without wishing to offend anyone, the skills) to analyse form based on collateral lines, weight, times, etc, etc, then I can understand why trends can be seen as a useful tool even though I often dismiss them.
They are a more sensible method of selection than guessing and pinsticking.
I've seen trends say things like the winner was rated 140-155 in races when every runner fell into that category.
I'm very guilty of responding to 'trendsists' by saying the only trend that matters is that the winner is always well-handicapped, regardless of weight carried.
Simon Rowlands used trends to arrive at Secret Reprieve but his analyses use different criteria to the lazy ones often cited. The main one he appeared to rely on for this race was the percentage of rivals beaten by horses rated within one or two pounds of the top by Timeform. In other words, the best handicapped!
In recent years I had both Elegant Escape (11-08) and Native River (11-12) top-rated, ie the best-handicapped in the race. The latter got into the race without a penalty for winning the Hennessy of all races!
Looking for lower weights in marathon handicaps makes perfect sense for reasons that involve the laws of physics but they don't win the Welsh National just because they're carrying a light weight. There were seven horses on Saturday carrying 10-7 or less. Four of them finished in the first six but you wouldn't have made a profit backing all seven.
It's fair to say Secret Reprieve was a bit of a no-brainer. The official handicapper told us as much. Whatever price he was was the odds about his staying the trip and having a trouble-free run. His SP of 5/2 suggested it was 2/5 he wouldn't win. I thought his chances were better than that.
In this case, trends were no more than a happy coincidence.