Excellent guide, I wish to God more people played by those guidelines.
I agree completely on the point of avoiding welding where possible. I do find it to be an extremely bad idea to rely on welding, simply resulting in a team's death. However, welding isn't a black and white issue, in fact you might want to update your guide with a small section on welding.
There are good place to weld, for instance in certain levels at certain camp spots, welding certain doors shut results in few to none zombies actually attacking the door. Instead the zombies will use alternate paths, resulting in fewer avenues to defend. Another good use of welding is if you're being chased by a bunch of zombies, make a temporary weld on a door (just empty your weld tool into it then run) to give you some breathing room.
An example of bad welding would be holding out with your back to a welded door. If anything goes wrong, you've sealed yourself into a dead end. Furthermore, if a decent sized wave spawns on the other side of the door, instead of coming at you in a piecemeal line, that whole wave is going to break through that door under cover of a momentary smokescreen and slaughter you. Another bad tactic is welding random doors along the map's main thoroughfares. All that's going to happen is sooner or later you or a teammate is going to be fleeing the horde and is going to run into a welded door and die (support specs, if you want weld points play office and weld all the small doors on the uppermost interior floor).
Long story short, welding used in reliance is a bad thing. It gets used as a crutch to prop up a bad strategy all too often. If used right, it's a useful tactic.
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