While the security advice is correct, it is possibly overdone for a private (home) LAN. Who is going to hack into it? The KGB perhaps.
If your internet access is from behind a NAT router then nobody can see your network unless you open up a load of ports including netbios and god knows what else.
The easy way to get in would be via the wireless access point (if you have one) but if you set up WPA/PSK then again nobody short of the KGB will be able to hack that.
In the end,
there is no security without physical security. What this means is that if you allow somebody to walk up to your PC unobserved, that PC is considered compromised. Somebody could install a keylogger on it, for example.
I'd share the lot. Makes life a lot easier
However, in my house I have a 14 year old who would hack anything he can, so he has his own account on his own PC and that account has no privileges on the other PCs. One can achieve that (using the login/password stuff) while leaving shares on all drives.