I am not a requirement engineer and do not write software requirements on daily basis. This story is written in software developers perspective.
Software requirements are the basis of all proper development work. You need them if you want to succeed. Unfortunately most of the requirements out there are incomplete or written, if at all, very badly leaving too many open questions for the developer actually doing the design and implementation. That is why every project should have good requirements that tell exactly what needs to implemented not forgetting error situations.