Packratting is the low end of the hoarder scale of 1 to 5. A house full of literally tons of garbage is definitely a 5 on the scale. Most folks find themselves down around 1 or maybe 2, and prepping can either exacerbate that or give you an epiphany about the amount of stuff you have.
Clutter can get in the way of a lot of things, and can keep you from doing important tasks, like finding your BOB and getting out of the house quickly. Clutter keeps you from having control over your stuff; clutter is stuff that controls you. Clutter can kill you if it is extreme, as in the case of the Class 5 hoarders...or, if nothing else, take room that you could be using for preps or other things.
The old adage about 'have nothing in your house that you do not know to be beautiful or useful' applies, but how to decide? Marketers know that if a sales person can get you to pick something up, put something on or try something out, you are more likely to buy it because the physical contact creates a kind of relationship with the object in your brain. Not good when you already have too much stuff. Maybe our moms were right when they told us to look and not touch in the store; maybe there's something that deep down they knew - that if we touched it, we would really want it, and our just looking was bad enough to generate a case of the 'gimmies'.
Decluttering is a way to remove from your life those physical things of little or no value that you are keeping for 'someday' or that project that's been sitting around waiting for time and/or inclination to start. Establishing order in your physical space helps with establishing order in your mental space, which can reduce anxiety. Here's an article from Zen Habits on how to identify clutter - and use the nine questions presented to help rid your space of clutter.
If you find it difficult to get rid of things, you could think of the process as removing everything to make your perfect home/BOL, sort of like Michelangelo and the statue of David. I know someone who's taken pictures of things she's gotten rid of, but that doesn't work for everyone; me, I'd gnash my teeth every time I looked at a picture, regretting that I'd gotten rid of the item, no matter if it had gone to a good home or not, because it would be a reminder not of the object so much as the <em>getting rid of</em> the object.
If you have ADD or ADHD, you might find that part of the clutter problem is putting things away, because out of sight can be out of mind, and you don't want to forget that project/item. I'm not that far into the book Getting Things Done, but it posits that if you get all the stuff in your head - the to-do lists, the 'shoulds' and projects, and write them down, you can get more done because you have an external, reviewable system to organize that data. That works for preps; nobody should be without a detailed inventory of their preparations.