A minimalist lifestyle can have many legitimate motivations. Sanctimonious anti-consumerism isn't one of these, nor is saving money. A laptop computer with a sizeable hard drive replaced my desktop computer, all my DVDs, all my CDs, all my books and (given a scanner too) all my paperwork. This isn't a "simpler lifestyle" in the sense that a laptop computer is simpler or cheaper than a book. In fact I still have all my DVDs and CDs in storage, in case I need to rip them all over again. Paring down all of one's clothes to point where they all fit on one clothing rail is good, but the reason it's good is not that an excess of clothes tarnishes the soul. It shouldn't be conspicuous and self-congratulatory. A minimalist lifestyle does not make you a better person.
But it may make you happier. It is not a weight off my soul, but it is a weight off my mind not to have too much to worry about.
I have very little storage space, so, the less stuff I have, the more room I have for myself.
I can't stand clutter, so the less stuff I have, the more space there is on the table for works-in-progress, and the easier it is to clear it entirely in preparation for a meal.
I get bored after staying in one place for too long. The less stuff I have, the easier it is to move. Not actually owning the house is also a big factor in that. I enjoy mobility.
I get irritable when my lifestyle has redundancy. I only really need two kitchen knives, why have seven? I only want to watch the movie, why buy the copy with the magic-draining "The Making Of" features? "I don't use this. Someone else could." "I never wear that. Someone else could." (Aside: Perl's motto is "There's More Than One Way To Do It". It's stupid. When you have to refactor a piece of code that somebody else wrote, they could have done anything and you have to be able to recognise everything they could have done. I prefer there to be one way; the right way. There is one Phillips screwdriver in my house.)
I like being able to find stuff. It's easier to organise a small amount of stuff. It's easier to find a specific thing when there's only one place it could be.
And the other thing is that, if I was held at knifepoint and told to decide, I'd be forced to admit that there are relatively few things in my life that (1) I'm sentimental about and (2) can't be digitised. I do go through old photographs and think "That was a cool time, that was a cool day with those people I know and love". But old clothes are just old clothes. Trinkets are just trinkets. The few concrete objects that I do love - mostly from prehistory, i.e. before 2000 - all fit in one big grey plastic crate, alongside the other nine under my bed which contain my stored DVDs, CDs and books. Maybe I'm broken in some way, or I've just grown up a child of the internet and electronic things are all that I really value, but a physical memento of that event doesn't pin me to it any more strongly, because what I really treasure is the memory of those events, and I have blog entries and photo galleries and video recordings which can just as easily trigger those memories, even after I've forgotten them myself.
In fact a physical object, to me, is a liability. Something physical can be broken or lost or burned down. Something electronic can be duplicated and backed up on multiple continents. It's a weight off my mind. I don't have to worry. If my house was burning down, and I could go and rescue one thing, I might not bother.
It is not possible, nor is it desirable, to own nothing. In fact, a point comes when not owning critical stuff (a bed, a toilet, a room) starts becoming stressful again, in a whole different way from "too much stuff" stress. "Simplicity" is a relative term, and perhaps inapt; try "convenience", which has more useful connotations. Fitting my life into a small number of boxes tucked under my bed makes me happy. Fretting over the precise enumeration of the items in those boxes would completely defeat the object of the exercise.