Reachmahjong.com

We already have too much pairs, even for full flush, so I don't see any real reason to keep isolated honors at this point.
For chii toi, we can make pairs with anything else, and it's always nice to have a regular hand as plan B.
Finally, one of the white is gone while our other single tiles are full alive.

it is. It's 1shanten for the chiitoi and only 3shanten for honitsu, so we have to maintain the iishanten. 3sou is of course dora, 4sou is vital for a honitsu morph later and our double-ton hasn't been discarded. With the amount of 25sou gone, the dora may very well get discarded later into a 9600 damaten. And chun dora1 isn't a terrible option if we need to get a quick tenpai.

By virtue of one being gone already. Chitoitsu, 1-shanten. Waiting to pair 3-4 Sou or Ton. Preferably pairing on the 3-Sou dora, asap.