What are the pros and cons of taking deferred admission in IIM Ahmedabad for a fresher? How much does work experience matter in IIM placements?

In general, it is a good idea to gain work experience before doing an MBA due to the maturity that gives you. At IIM Ahmedabad, a lot of placement opportunities ask for at least 18 months of work experience depending on which field you are opting for. If you are a fresher, you are going to miss out on those opportunities. 

So, having work experience is definitely an added advantage. It does not sound like a good decision if you are going for a Masters in Business Administration and have not been to any workspace personally. Peer learning is an integral part of management education. You will be able to contribute more to that only if you have valid word experience. So, it definitely makes sense to defer for a fresher or student with less than a year of work experience.