guest book for eng party??

What is the purpose for a guest book? Should I have one for the eng party also?

I was thinking of getting one of those fishbowls for the wedding time for people to put little notes or bits of advice on married life in addition to the guest book- should I do the fishbowl for the eng party instead?

i would save the bowl for the wedding - just because it's usually for people to write marriage advice or tips .. so doesn't make much sense at an engagement party?

we didn't do a guestbook at our engagement party .. but we're doing the wishbowl and a normal guestbook at the reception.