Summoned Servitor's niche. While the resource cost isn't bad, its asset discard cost means it's unlikely to be one of the first cards out of the gate, and its dual slot cost is another barrier. In practice, Summoned Servitor is going to cost at least 3 XP. Without at least 1 XP, all Summoned Servitor can do is hover around the map. And while 1 XP is enough to start taking some actions, it's hard to find someone who wouldn't want Dominance to free up a slot, one way or another.
From there, there are a few directions for the summon. The first and most apparent through the test actions. A 4-base test is okay, if not particularly impressive - you'll occasionally stumble onto a success, as long as you're willing to fail along the way. Of course, If someone runs Rabbit's Foot, Drawing Thin, "Look what I found!", or the like, even a failure can be good. And characters with easy boost access, like Charlie Kane or someone with Cornered like Patrice Hathaway, can turn those awkward checks into something that resembles a bonus action. Daemonic Influence can technically give even more 'actions', but it's one of the most expensive customizations around, and quite possibly one of the most difficult to build around.
The second option is to use Wings of Night as the equivalent to Pathfinder or Safeguard. While Summoned Servitor's movement isn't particularly mobile, it can still move one space a turn - and that means that if you don't need to move more than one space a turn, the summon can save that move action for you.
The third option is to use Armored Carapace to treat this as a source of soak. While a few scenarios may make you regret this decision, it's often a cheap plus. Armored Carapace allows you to share the soak, but it's worth remembering that investigators can assign damage to any asset under their control with health, and the Servitor is always under the investigator's control, no matter where its location is. It can tank for others sometimes, but it can always tank for its player.
And, of course, there are always a few incidental benefits to this. As one of the options, it's worth remembering that investigators who access this can boost it using Down the Rabbit Hole. And some people just want to squeeze a bit more XP through Refine.
On the whole, I don't think any of these single options is worth the total card, resource, slot, and XP cost. However, if you're looking at a couple of these, you might be breaking even or earning a bit more. Some classes may have better options, but for some or off-, you might just be looking for the combination of a bit of health, or an extra action, one way or another.