In short, it means you don't have to worry or think about what to wear. You know what you need to wear and people can't make fun of you for your fashion choices.
Though, actually,I don't think it should be mandatory as you say, it should be up to the school.
Data has shown that students in schools where uniforms are enforced do better. In addition to this, dress codes or uniform policies help alleviate the stigma faced by children from lower-income families, whose parents may not be able to afford nice clothing and who may be teased or bullied as a result. Uniforms make all the kids look the same, so that attention is focused on how they perform, rather than what they are wearing. Not every child's family will be able to afford uniforms, and for this reason, schools that have uniform policies should provide their students with the uniforms they are to wear.
Having uniforms in schools can be a very constructive thing to many kids, though they should not be mandated in every school for the entire time. Uniforms can take away some of the ammunition of those who want to bully, in addition to focusing the children and creating group cohesion.
I think that schools and districts should be able to decide for themselves whether they think that school uniforms are the best option or not. School uniforms are something that a lot of parents like, however, since it helps keep the costs for clothing from being too expensive as well as easier in terms of deciding their kids' daily wear.
If people want to pay to send their kids to a private school that wears uniforms. That is for them to decide. The rest of us should not be forced to do such things, because some people thinks it makes their kids more well behaved. It kind of takes away from the kids creativity in my opinion.
I don't believe that kids should have to wear uniforms because it takes away from the freedom of expression that kids have. They identify themselves with what they wear and have the first opportunity growing up on how they want to look. I don't think uniforms make kids be better or worse so I would stick with no uniforms in schools.