Will internship be of much help?
Yes. It helps. Internship not only give you practical experience of the real world, it gives you a chance to check out if the higher studies / major you intend to take or you are taking is correct or not.
For eg., if you are in your graduation and doing your internship in finance, and you find the work and things to learn on job very much interesting, you would gain more confidence to do your Masters in finance or MBA in finance. If however, you find it not so interesting and motivating, you can look for an alternative post graduation degree, other than finance.
Hence, in such a scenario, internship while graduation is a better option than during masters, especially if you are unsure of the higher study specialisation you have chosen or plan to choose.
Doing an internship anytime is always an added advantage. With so many students passing out every year with graduation and post graduation degrees, you need something to show on your bio-data to stand out and be selected.
A company always prefer, apart from your grades and college background, someone with a bit of work experience. It saves their time in imparting trainings etc., to a fresher. Getting the work done rightaway from day one is what every company expect in our country. So a little experience is always a plus.