Subdomain or not subdomain

[hkindc]

As we develop a new site, we want to keep a lot of new informational pages on a sub domain. Our blog is on one and we get extra listings on google from it with every post- google will give 2 listings per sub domain, supposedly. Our new design firm discourages this claiming that this weakens the main domain. Our domain is pretty strong on its own organically and so I think folding out new informational pages- key word heavy and link heavy- would be a good move. Maybe they just don't want to do the work of carrying cookies across from domain to sub domain.
any opinions from the experts here?
Thanks for any help

[newbie2010]

Many times it create complications, so batter is to have a new domain by some more $$$.