It's extra challenge in an extremely arbitrary fashion and lends itself to stealing everything that's not nailed down in case you run into a traveling trader or somebody else with caps.
The only way to even argue it's "extra challenge" is to argue that hitting pause to go get a drink or take a leak is challenging. I mean, we're basically talking about a book keeping task in this case. That's not challenge. Having to cart 3 loads out of Vault 13 because you want the guns for extra repair fodder isn't any more challenging than using Excel.
So basically you are right, I am wrong and you don't at all care about people who actually do like the system. Well that puts your opinion into perspective.
No it's more that MOST gamers are horrid at putting this kind of shit into perspective. I'll exclude EVE players a simply state most gamers don't like working in Excel spreadsheets. If I start adding line items to Excel "rusty boots" and "vagabond outfit" does it become more exciting? Nope. You can add all the flavor, which is probably what you actually enjoy in these systems, in ways that don't add an arbitrary book keeping system to the game.
While restricted inventories might be a pita if they are to restricted, they often enhance gameplay in my opinion.
I think it is essential that you don't pick everything up
. That was one point that made New Vegas so much better than Fallout 3. Now that ammo actually weighs something, makes you think about your load-out and what is important for you to pick up.
And then they contradict their own "Hey you don't need everything" hints by making you need: a fuckton of guns/melee weapons for repairs (or a way to earn massive amounts of caps), throw loads of shit around for you to pick up (gee, I wonder what will be useful/valuable, better check the wiki), put in a quest that requires you to bring a bunch of scrap metal to someone (something you'd only have kept around if you were crafting) and a bunch of other dumb stuff.
Fallout 3 and NV are examples of getting it 98% wrong, you're already allowed to carry between 200 (or more) pounds of stuff and still jump, fight, and run for miles, there's no AP penalty for being overburdened in a fight, they could have done away with most of it and had the exact same game.