when is the appropriate time to use [? and :] instead of if statement?

ok so i've seen [? and :] used in as replacement for some if statements in a lot of code

for example

driftDirec = Input.GetAxis("Horizontal")>0 ? 1: -1;

why not something like

if (driftDirec > 0)
{ do stuff}
else
{do stuff}

or something, can you tell me when is the appropriate time to use those and i don't know what that's called?