This is also called a post-oak bluff. I think it has its place against weak/tight players, but isn't effective against solid or aggressive players (or loose calling stations obv). A 1/4-1/3 pot bet only has to be a bluff more than 1 in 4 or 5 times to make calling profitable. So as the post-oak bluffer, it has to be a value bet more than 3 out of 4 times, in which case you're losing a lot of value on your value bets. Make sense? Put another way, if your small river bets are usually bluffs then people are going to figure that out and they won't work, and if you make small value bets enough that they aren't sure, you're losing $ you could have made by value betting more.