Hi knightrider,
In physics, the examiners don't clearly tell us how marks are awarded and teachers often judge answers based on their own expectations. The exam reports are not in-depth and usually only present one interpretation especially for worded questions.
My advice would be to show as much working out as possible so that the assessor can see if you made a careless error, and therefore be more inclined to award you marks for demonstration of the correct physics principles.
So for projectile motion, I would write the 'shortcut' formula, then write it again with the known information substituted in and then solve and write the answer. Assessors are familiar with these formulas, and if you use them in the correct situation but just enter something wrong in the calculator, you may only lose 1 mark as they are aware that you knew what you were doing.
However, if you use the 'shortcut' formulas when they are not applicable and as a result get the wrong answer, you will not get marks.
Lastly, to address your point on the traditional method of dealing with projectile motion: It may take too long in an exam to set all your equations up and will not be advantageous in dealing with a question that the 'shortcut' formulas can be used for. Some questions, you have to set it out the long way, and method marks will be awarded if you demonstrate correct physics principles.
As long as you demonstrate an understanding of the situation presented to you, and apply relevant and correct physics ideas, then you will most likely gain some marks with or without a correct answer!