Whats the purpose of an inline pump?

[str8stang036]

I wanted to know what the purpose of an inline pump is? Because lets says you get a 255lph intank what purpose would the inline then serve?

 

[mr_woodster]

its the *just in case* pump

 

[S/CBlack95GT]

Basically they help the intank pump to maintain a higher pressure. The intank pump pulls the gas out of the tank and the inline pump pushes it to the engine at a higher pressure, therefore the intank pump can work more efficiently.