They are incredibly useful. The Wizard in my party has his own Hawk familiar for scouting and other various tasks like carrying messages or spying.
Then I made it worse by giving him an enchanted robe made from Raven feathers, that allows him to summon up to his proficiency of Ravens for no component cost. (if they are lost they take each a day to come back. And only one per day so two lost means two days to get both of them back)
He does use it as an attack platform some times, but I think that is probably the most boring of uses. He will give them good-berries to pass to any downed party members, which is a pretty good idea as well.
Good as distractions.
I have seen the video linked. I always find his advice as pretty solid.
Scouting is the most common. They don't have attacks unless you somehow get a special familiar. Remember they can still make checks so potentially pick pockets and deliver your spells as their re-action.