Chelsea Manning on war and embedded journalism in the Times:

‘The process of limiting press access to a conflict begins when a reporter applies for embed status. All reporters are carefully vetted by military public affairs officials. This system is far from unbiased. Unsurprisingly, reporters who have established relationships with the military are more likely to be granted access.
Less well known is that journalists whom military contractors rate as likely to produce “favorable” coverage, based on their past reporting, also get preference. This outsourced “favorability” rating assigned to each applicant is used to screen out those judged likely to produce critical coverage.’

(Read the article here.)

I was embedded with the US Army in Iraq twice, in 2008 and 2009. (Read one of my articles in English translation about this embed here.)

Compared to my embeds with the Dutch and German army in Afghanistan (2006, 2007 and 2011) I would say that the U.S. army was much more relaxed in Iraq than their Dutch and German counterparts in Afghanistan.

But of course, the main reason why an army would allow journalists access to their war zone is the hope on positive coverage.
An embedded journalist will sooner or later identify with the unit he is traveling with.