STEM subjects can be thought of as requiring basic knowledge of the sort usually gained in a first degree, which then has to be applied. Most practitioners will follow a career that applies their knowledge rather than develops it further. For example, pure maths develops the subject and expands it whereas applied maths uses the output of pure maths and applies it.
For many applied subjects it is necessary to interface with another discipline. For example, for a geologist to work with engineers, miners, bankers, lawyers, insurers and environmentalists it is usual for a geologist to seek further education for this transition: that would normally involve taking another degree, a higher degree, in some aspect of geology.
Higher degrees which provide this education usually offer it as a Master Course (MSc not MSci) in a particular discipline. Traditionally these require 12 months of study and exams.
Care should be taken before enrolling on to an MSc to ensure that it will be accepted by those areas of industry and commerce that appeal to you and into which you want to develop your career. Seek advice from potential employers about the sorts of MSc qualifications they seek and accept. The safest time to embark on an MSc is once you have gained a few years industrial experience in the area you wish to work.
Many do not have this luxury and they should be careful that the MSc they choose will deliver the step forward they require. The Colleges will invariably advise that their course is exactly what you need – BE CAREFUL.
It also makes your life a lot easier in later life when you apply for Chartership if you have attended a course of study which is recognised by the professional body for your discipline.
It is important to realise that the MSci degree is not equivalent to a post-graduate MSc. An MSci is a 4 year undergraduate degree; an MSc is a one year postgraduate degree.