Reverse Proxy

I got few doubt about using a Reverse Proxy as a added Security Measure 

1)  how good is the idea to  use of reverse  proxy as a layer of defense while 
accessing a web portal .

2) Should it be consedered majorly for security as it provide Single point of 
access and hides internal servers and because 3) Is there any other particular 
feature because of which we shold always be recommended it as a added layer of 
Security .

3) or is it  something mostly used for Caching and Load balancing which also 
can providing security feature mentioned above like single access point and 
wont actually contribute much in making a network architecture secure .
by hiding the addresses from world and acting as a single point of inspection .

4) If it is used what is the major consideration should be take place in its 
implementation to ensure Security .

5) What are some best known and used Revrse Proxy products apart from the well 
known open source one .

Regards
Zack