I have been doing airbnb for 33 months. 176 reviews, 190 or so stays, multiple repeat guests, 97% 5 star reviews, almost 14% booking rate, superhost for 10 straight quarters.
I've used instant book for the last 2 years and I've pre-approved everyone who has inquired rather than instant booked.
It really depends on what kind of rental one has and where you are located. New hosts probably should not instant book right away if they are given the option but once they learn their market instant book might work for them. Some new hosts are not given the option, they are forced to have IB. That doesn't mean they can't be successful.