Are transition strips necessary in doorway for laminate?
Yes there are a few tricks. 

Lay out the flooring to find where the joints will finish at the door. If the run to the door is really far away, it can be done, care needs to exercised. You want to cut the starting piece to allow a lang seam to happen with in the width of the door jamb. 

First, the door jamb and trim are cut to allow the flooring to slide under it by about 1" Cut it and check it, be certain it goes in at least close to 1", 3/4" is acceptable, no less. Also, at least on these pieces, make sure the length will slide under the drywall to the plate (1/2") as well. If base is in place, at least a 1/2" there, but it is really worthwhile removing the base everywhere first. The job is SO much easier.

Typically the pieces going in the door will be large exaggerated "L" shaped pieces. But for this it does not matter. Start laying the last 2 runs together. When you get to the door, set the piece under the door jamb first, pushed tight to the wall to allow the next to the last row to go in, Before that piece is set, you will need to determine where the piece in the door will engage it. That part of that piece will need to have the lip removed so the door cut can simply slide in place with glue in place. Use lots of glue and clean up the excess. Dry it and hold the joint together with 3 or 4 pieces of painters tape, the wide stuff. This approach works whether the butt joint is in the door or not. To finish the door, depending on the type of laminate you will only need to remove a portion of the lip where the angle to lock it in cannot be done, and keep the lip were enough warp can be made to lock it in, using glue where the lip was removed. You may be able to warp the first pieces going into the door as well. That depends still. It will save some gluing if you can.

Thes last pieces at the door can be done first as you go into the next room, once the door is finished, the other pieces can be back filled in.

Word of caution, when going through a doorway and establishing the true course the floor needs to run, get a long reliable straight edge to set the run going into the next room. Do not let the floor dictate "what is straight" It will mess you up. At the most you can set another piece to the pieces going from the door to get a line a little farther from the wall, but a critical line needs to set by a straight edge.