Ferret best practice

Hello,

I am searching for Ferret best practice : when to open, close, and
optimize a ferret index on a classical web application where many people
add, read, and sometime delete elements.

Do you always keep your index open ? or do you open and close it on
every transaction ?

Do you optimize your index often ? on every insert ? on every 1000
insert ? or every night ?

Thanks for you feedback
hakita