Every part should have sketch(s) that is fully defined and extremely easy to edit, always remember, at school no one will read your sketch, not even the professors for grading, but in CAD, especially CAM firms other engineers and technicians will need your sketch to be as clear as possible and as much easy to edit as possible.
Use relations and construction lines, instead of dimensions where ever
possible, NEVER link part sketch(s) to external (other) parts in an assembly;
it is considered a very bad practice everywhere! Because if someone goes in and
changes the "external" part, the original part changes due to this,
which messes up the whole assembly.
Fully defining a sketch, it is always easy to just whack dimensions
everywhere, but fully defining properly takes a lot of time which means a lot
more money to the client to pay but stick with it, remember it is you who have
to modify it later if needed, make a fully defined sketch now and save the
trouble later.
The only way you would not fully define a sketch was if you are doing
"recreational" modeling or something. In real work always define the sketch.
It is a nightmare to make changes (for others) to parts that were created by
you by using sketches that were not always fully defined. Being able to edit by
another engineer should be a high priority.
Minimize the use of 3D sketches.
