NOTATIO

My old composition professor recommended that we enter dynamics at every rehearsal mark even if it was unchanged - this way if the players were rehearsing and starting at a particular rehearsal mark they would not have to scan back in the score. This was about 10 years ago.

However, Dorico 6 new proof-reading feature flags this as a possible error.

I know that there are many discussions out here suggesting that rehearsal marks are obsolete and that bar numbers are more than sufficient. But aside from that, are there any any thoughts/suggestions?

This "practical" suggestion sounds quite impractical to me for two reasons:

1. It could lead to a lot of second guessing on the player's part: Why is this p here? It's been p. Did I miss a previous dynamic change? So the extra dynamics would probably need to be placed in parentheses to show that they are precautionary. Which then leads to no. 2 following.

2. The clutter of all these extra dynamic markings either plain, or even worse, enclosed in parentheses.

But perhaps this is actually done in some genres?

I would consider it unnecessary clutter, and confusing (for the reason John Ruggero suggested).