If you can do so without spending a fortune on photocopying or doing injury to your back, it is sensible to arrive at the tribunal with more copies of all the relevant documents than you expect to need.
If a few copies of a schedule of loss or witness statement stay in your bag throughout the hearing, no harm is done. But running a case when some people don’t have all the documents is a serious pain. So it is best to err on the side of caution.
Also, documents do get damaged or lost – particularly over the course of a long hearing. If a tribunal member manages to spill water over his chronology, it is handy to be able to pass another copy up.