Should teachers enforce standardization of spacing and braces? On open source projects and industry teams, there are often detailed style guides about how many spaces should be used for indents, line continuation, etc., and whether braces should go on their own line. While I have my preferences (such as spaces around binary operators), I acknowledge they are somewhat arbitrary. Should I require students to follow a standard for assignments and team projects (perhaps conventions of their own choosing), or should I ignore these as trivialities?

Of course, I would enforce more important conventions, such as proper indentation, appropriate naming, etc.
Our two deities are clarity and efficiency.  

Standardization makes a great deal of sense in industry, where large numbers of programmers may work with the same lines of code and must be able to make sense of each others' choices. However, I don't see value in enforcing particular style guides in an educational setting.

Different companies can require different norms.  If your students eventually enter the industry, a style guide is easy to read through if they can code, and is irrelevant if they can't.

When I teach my kids to worry about indentation, vertical spacing, variable names, etc, I teach them to always use this question as their foundation and their guiding star: "what does this choice communicate?"  

That is honestly already quite a lot to tackle, and I have found that my kids really do start working quite hard and thinking quite deeply about how to make sure that every line of code is as clean and clear as it can be.  

If my students can learn to scale this mountain, why would I ask for 4 spaces in place of a tab?