With a ton of RBs and WRs coming off of the board in the last two rounds, you could see a mini-run on QBs and TEs in Round 4.
At this point, most of the WRs with WR1 upside are off of the board and all of the RBs left have question marks. What you do in Round 4 will somewhat be dictated by what you did in the first three rounds. This might be you last chance to get one of the high-end QB1s or TE1s.
If you've drafted a QB or TE before this, you're going to find yourself scrambling to fill either your RB or WR slots. That's okay. When that happens you're going to go for a "quantity over quality" strategy where you grab a bunch of RB/WR with some upside and hope that you hit on one or two of them.
For reference, I will be listing each player's Expert Consensus Ranking - PPR as determined by Fantasy Pros.