I don't like having a cluttered classroom. Boxes and papers stacked everywhere. Too much furniture.
This clutter impedes the flow of children and adults. It is also a safety hazard in the event of an emergency evacuation. Clutter can also prevent the teacher from surveying the entire room at a a glance, and you always want to see what is going on.
The idea of reducing clutter also extends to "visual clutter". Walls and ceiling cluttered will all kinds of distractions. Especially in the front of the room where you teach from. This may look festive, but ...
Too much visual stimulation is not conducive to promoting concentration, especially for those students who have yet to develop their attention skills. If a student needs to look up and around the room to get needed information, concentration may be interrupted.
I put helpful information on each student's desktop. Using desks helps students learn responsibility for their own space. Each Friday we have desk cleaning to make sure the desks are emptied of papers, old bananas, etc. and then wiped down. There are many commercial desktop helpers you can buy (from Really Good Stuff and others). I include an alphabet sheet, a letter sound sheet, the student's name, hundred chart, number line, etc. I laminate the sheets and tape them down with clear box tape.
Encourage your students to find the information they need without looking up. Teach them strategies they can use to figure things out for themselves ("Use the Clues"). Supply these materials for home as well, and instruct parents on their use. Check with the next grade level teachers to see if they will allow your students to keep copies of these materials with them while they transition to the next grade.