Why the Bengals would do it.
A lot of mocks I have seen have Cincinnati picking an LB at #21, this would still leave them with a big holes at Safety and RB. At #37 they could easily get one of this draft's top RBs and may want to stay put for that reason; however moving up would likely allow them to grab one of this draft's best safeties; Kenny Vaccaro and Matt Elam seem to be consensus first round guys, while I've seen Eric Reed all over the place in the first two rounds. They also need a CB and this trade could put them in a position to grab either Jonathan Banks, Xavier, Rhodes, or Desmond Trufant; all of whom look like they will be good players at the next level.
Why the Dolphins would do it.
Miami needs help at a lot of different positions. Like A LOT of different positions. Honestly a case could be made for DE, LT (as it looks like they may let Jake Long go), WR, CB, or even TE as their biggest need. With all of these needs they may not want to give up one net early pick, but then again, the chance to grab a good player at a position of need before the talent drops off could be too much for them to pass up. Trading up to #23 would give them a multitude of options. They would likely be in a position to draft Lane Johnson, Tyler Eifert/Zach Ertz, one of the CBs listed previously, or one of many DEs (Sam Montgomery, Alex Okador, Ezekial Ansah, etc.). They could also be among the first to grab a WR and get the guy that they prefer.
Why the Vikings would do it.
The Vikings are the reason we are all here. We know their needs (WR, DT, and LB in the top tier with OG, CB, and backup QB being second tier) If the trade were to go through with Cincy, we would get picks #37 and #55 on top of our own #54; if it were to go through with Miami, we would get #43 and #56, again along with #54. Either of these trades would allow us to grab at least one WR and one DT who may have gone much higher in a less deep class. Then we would have another second round pick to which we could use to pick up another WR, an LB like Arthur Brown or Khaseem Greene, an OG Like Alvin Bailey, Barret Jones or Larry Warford, or even a CB like Jordan Poyer, David Amerson, or Logan Ryan. This would also free up our #85 with quite a few options. Without this trade we are almost locked into taking WR, DT, and LB in the first three rounds (in no specific order and assuming we wouldn't have to make a ridiculous reach); with the trade we would have a lot more flexibility and could still get quite a few good players from such a deep draft class.
Tell me what you think; would you like the team to make a trade like this, or would you find it to be a mistake?