When to use hyphens in compound words

Solution 1:

The most important thing in writing is that you are understood. People need to know that a compound word is in fact is a compound word if they are to understand it correctly. For compound words which are not frequently used or could easily be mistaken for something else, you should use hyphens.

When there are 3 or more words connected together, I'd use hyphens. In the case of cross-sections vs cross sections, many people are familiar with the term so you could take out the hyphen, or you could leave it in to be more clear. Just be consistent in your decision to keep/leave it.