The underwriter's goal is to facilitate a successful IPO. There are obviously different interests at play. The company and its investors would like to say as high a price as possible. The new public investors the shares are being sold to would like to see as big a profit potential as possible. The bank's job consists of choosing a sensible price point for all parties involved and advertising the offering so as to generate interest in the shares. Once the actual IPO happens, the public is able to see whether or not the bank did a good job. This in turn is important for the bank's reputation and ability to acquire future deals.

The FB IPO was widely considered a failure because the initial share price was unsustainable. The underwriters had to buy massive amounts of shares on the IPO day to stabilise the price above the initial level. This, however, couldn't avoid the crash over the next months which lead to early public investors being underwater. Morgan Stanley's (as well as Nasdaq's) reputation took a big hit thanks to this and it will haunt them for quite a while. It's also the reason why the TWTR IPO is lead by Goldman Sachs and the shares trade on the NYSE.