disadvantages of not putting "doctype" tag

[Pejman]

my question is about designing web pages but not necessarily in Publisher.
what disadvantages, not putting "doctype" tag at the beginning of webpage
may has?

 

[David Bartosik - MS MVP]

you'd want to refer to
http://www.w3.org/
It's stating what standard your code is supposed to adhere to.
Not having it does no harm.