You do light 3D mechanical work or need parametric constraints but cannot justify the $2,000+ for a full AutoCAD subscription.
You only need to measure PDFs, print drawings, or teach a student the basics of CAD.
For the professional seeking a permanent, low-cost alternative, nanoCAD offers the best price-to-performance ratio on the market. It isn't "cheap" in quality—it is simply priced for engineers, not for Wall Street shareholders.