Use relayhost or not ? What is the best strategy ?

[Pierre Couderc]

In old days, using relayhost was a good solution for ISPs who declared 
an IP as dynamic even when it is static (free.fr did that..) .

With the inconvenience of ISP smtp IPs being blacklisted because of 
spammers.

Is there a good reason today to use relayhost ?

What is the best strategy ?

Thanks

PC