When you export a Layout file to PDF the resulting file size is very large, even when selecting Low quality. I have found the best combination is to use the Medium setting and then compress the file with online tools like SmallPDF or PDFCompress. When doing this the resulting quality is excellent, but it adds an extra tedious step. It would be nice if Layout could handle PDF compression well, perhaps with a variety of options (that remain persistent from session to session — see my other feature request about session persistence).
For example, my typical template results in a file of 10Mb when exporting a 3-page file with the Medium setting, and once compressed it is down to about 600Kb with little detectable loss in quality.