You can animate a rigid 3D model by specifying node transforms, key-frames and timings. For example, a car engine can be animated using just rotations and translations. GLTF supports these types of animations but it seems that UE doesn’t import those. Sometimes you want a pre-baked node animation to play on demand.
Does UE expect all animations to be the “skin-and-bones” type or is there a way to import and play node transform animations?
Should simple animations be transformed into rigs? Isn’t this overkill?
We made our own system of transform animations for static mesh animations like doors, buttons, hatches, levers, elevators, etc. that can be easily set by code or some variables in details panel.
Performance wise, if it doesn’t need to be skeletal, it should not be skeletal.
I’ve not looked, but if you don’t want to roll your own, there’s probably some static mesh animation systems in the store.
Or I guess you could use TimeLine? But that seems a bit complicated for buttons, levers, switches, doors, etc. Not sure. 
I have a custom system for moving and rotating actors which covers stuff like windmills, doors and pistons. So simple animation where only a few things are happening and might be repeated.
I’m now thinking about how to handle more complex animations that I don’t necessarily want to hand-animate in UE5. Ideally I could import an animated asset from DCC software, for example a GLTF steam engine, and it would automatically be translated into UE5.
I am constantly surprised at what UE5 seems to expect users want.