Think about this with common sense.
- If you will write your password down - then it can be found and read by others unless stored in really safe environment;
- If you will not write your password down - there is no possibility for someone to find it and read it from the paper.
Also, passwords for different accounts must be treated in different ways. Password for your banking account should be secured more carefully ( or not less ) than password for something which is not critical ( i.e. on-line game).
Password itself is useless. Data and account secured by the password - these are things which should serve as criteria of how much effort should be applied in order to prevent anyone finding out the password.
As example - I would not mind write my password from WI-Fi access point at my apartment - because it is fine with me if someone who lives with me will find out this password.
But I will not do this with password for my e-mail - because it is not fine with me if anyone but myself will access it.
In addition to that a general rule which can be applied here is:
Every time you are typing or writing your password (would it be login procedure or writing down your password) you lessen its security just because it left your head and now exists as written thing which can be read or gotten by sniffing network traffic. Hackers will have more chances to sniff your password if you log in over the network 70 times per day. If you log in once in a month they have less chances to get it.
Same thing with written down passwords. Every time you write it down its security lessens, because now it also exists outside of your head.