In my opinion, it is always best practice to model about the model origin and to make use of symmetry whenever possible.
Dynamic Mirror Entities:
The easiest and fastest way to create symmetric elements in a sketch is to use the Dynamic Mirror Entities command. It works like the regular Mirror command, except it automatically creates the symmetric elements on the fly and applies the Symmetric constraint.
The tool is categorised as a Sketch Tool, so found under the Tools dropdown. But can also be added to your sketch command line through the customise tool, and of course you could assign a keyboard shortcut.
To use this tool, you must first sketch a construction line along the line of symmetry, preselect it, and choose Dynamic Mirror. The command is active until the sketch is exited (you can tell if the command is active by the “=” marks at the top and bottom of the centreline.) If you re-enter the sketch, the command is no longer active, and you must reselect the construction line and run Dynamic Mirror Entities again.
By Jon Crookes
Elite Applications Engineer