Weefle Day attempts to constrain the players to a limited amount of money and attack/defence capability.
There are actually only four rules:
Rules 2 and 3 seem to be similiar but they allow some flexibility in the presence of X-to-rez Ice and prevents Corps using a Rent-to-Own scheme that will completely shut out the Runner (vide below).
Regarding rule number 4: Efficient running is the key here.
Apart from that there are few differences in the format. The analytical in the playgroup may find that they can build the "unrunnable" fort, but if that is what they want, Roving Submarine can do the same job, so there's little worry there. A smart runner packs a few Ice destroyers anyway, just in case the megafort shows up that stops them getting through.