I'm going to throw my husband under the bus here. When I get the decluttering bug, one of his frequent excuses (other than "but I use that") is "but we have the space."
Not surprisingly, I do not find this a justifiable excuse. I feel so much better in uncluttered spaces (to be honest, so does he). So having space to keep clutter does not justify having clutter.
I find that when I declutter spaces where I "have space," I free up room throughout the room or even my whole house. For example, when I discarded expired ointment and a medicine dropper from the medicine cabinet I was able to declutter the bathroom counter. I now have space for my deodorant in the medicine cabinet. My daily environment is less cluttered because I cleared out a space that was hidden. Although I "had space" for those unnecessary items, decluttering allowed me to prioritize valuable things above undesirable things.
This is true for anything. Deluttering the garage, the linen closet, the cabinet under the sink allows me to get rid of the things that aren't really valuable. This may allow me to store something I find valuable (I like to store the swim things together during the summer, in the linen closet, so no one loses a swimsuit and we can walk out the door to the pool without hassle) or it may allow me to simply enjoy a clean counter, dryer or other flat surface.
Sometimes I don't see the point to decluttering invisible spaces. If we've "always" stored table linens there, why should I declutter them? We're not going to stop using tablecloths and napkins, after all. But the last time I decluttered that space I found two tablecloths that I didn't even realize we had, and now it's easier to find what we actually need.
I know some people like to declutter their home in one fell swoop. I'm the other kind of person; I keep whittling down my unnecessary possessions until I (hopefully) have a minimalist home with nothing in it except the things I find really important to the way we live. Hopefully a day will come when I do not have to worry about cluttered surfaces, cabinets or drawers. Even better, I hope not to have a cluttered mind. In the meantime I will continue to declutter both the hidden and visible clutter, whether we have room for it or not.