On my first N scale layout, which was code 83atlas and peco turnouts. I did solder everything, which made it strong and bullet proof and I ran a feeder about every three feet. everything worked ok, but when it came time to remove the track or redo an area it was a mess on the turnouts.
My current layout is also N with code 55 atlas track and flex. I have only soldered in a few complex places and still drop feeders every three feet. I have no operational issues. I have a few little gaps as the track is placed and cut by my crew and it doesn't bother the locos. not soldering has saved my butt already when I damaged a turnout and had to remove it and replace it. slid the joiners to the side and took out. my layout is not large or in a temperature controlled room, so it gets cold and hot in my garage and so far my trains run good. I DO solder in my helix if the joint is in the curve. Several of my round robin guys which model in N and HO have large layouts and we do not solder either. no issues either. I guess its built in expansion joints.
good luck.