If a modder can get touch spells to work through the familiars I'd certainly consider using them more.
For the basic familiars the best use I found was to get close to an enemy so Astarion can utilize sneak attack.
They also work well for scouting. Fun fact if you can get a familiar to a warp portal it counts as discovering it for your team to warp to. I used that to warp into the Selune Temple in the UD after entering from the spider's lair.
