There are many great pages written on this topic. An older but relevant article from Matt Cutts: http://www.mattcutts.com/blog/seo-advice-discussing-302-redirects/
In short, a 302 would only ever be used if the move was temporary. You are correct in that they do not pass a link's value. I would only use a 302 to resolve a temporary problem.
A 301 passes 90%+ of the link's value, but there is some loss. That is why you would prefer not to use it, especially if the move was temporary. Using multiple 301s in a chain can be especially bad for this reason.
First thing I was wondering about, was the use of a redirect to a new site using an additional directory /content/... Why would anyone do this?
There are some very good reasons. It sounds like they originally had the site located in the root directory of their web server, and did a re-organization of their file structure. Their site is now contained in the content directory. Perhaps they set up a new CMS which required this change.
The most logical structure would be www.domainA.com/products/.., and not www.domainA.com/content/products, right?
It depends on your perspective. For example, if you have a WordPress blog site or other CMS paired with forum software, then the wordpress site is often set up at the root domain. The forum software would be in a directory such as /forums or perhaps /content. If it was my site then the products would be located off the root directory as you suggest, but others could certainly offer it within the /content directory.
what are the actual implications when redirecting from domainA.com to domainA.com/content?
It depends. A well established site will often have a lot of link value for their home page. That value would be lost with the 302. There is nothing specifically detrimental per se. It is more of missed opportunities.