If you're not familiar (sorry) with 1e familiars and how they work, let's just say they're in general a high-risk low-benefit proposition most of the time for a field-adventuring mage because when it dies - and it will, guaranteed! - the caster permanently loses hit points* equal to what the familiar had. They are, however, a great thing for a stay-at-home mage type who never puts the familiar in danger, as while alive the familiar gives you enhanced sense(s) and adds its hit point total to your own maximum.
In general, once the players realize the long-term risk involved familiars come off the table real fast.
* - how the hit point thing works: if a mage with 14 h.p. casts FF and gets a 4 h.p. familiar the mage's max h.p. becomes 18. However, when the familiar dies (unless it dies of old age) the mage's max h.p. drops to 10 - you lose what the familiar gave you plus the same again
Thanks! Vote amended.