Most importantly, it will tell you where and when the tribunal will take place. This sounds obvious. It is, but people do get it wrong. If you rely on a conversation with a collegue or client, you risk that he mispoke or you misheard. Make sure you see the notice of hearing to be sure.
The other pitfall to avoid is that some of the smaller hearing venues are administered elswhere. Brighton, for example, is administered in Southampton. So letters from the tribunal will have the Southampton address. It is easy to assume that the case will be heard in Southampton. Again, the notice of hearing will put you right.
In addition to time and place, the notice of hearing may contain other useful information. It will say whether you are expected to deal with liability and remedey, or liability alone. If you are actually listed for a Pre-hearing Review it will say so, and should give some indication of what issue will be dealt with.
You should always see the notice of hearing in any case you are involved in. If you do not have it, get a copy.