^That's the idea, though to be more precise it can handle your base vertices and 4 additional targets (so, 5 if you count the base vertices).
Technically I compare the morph weight with an epsilon (~0) to decide if a morph should be used or not.
Here's another answer I gave a while back https://forum.sketchfab.com/t/help-us-test-blend-animation-uploads/6228/31?u=stephomi
If you decide on using many targets beware of the weight interpolation. For example let's say you have keyframe "1" with morph 1/2/3/4 and then keyframe "2" with morph 5/6/7/8.
You might think "well it's ok", but during the interpolation between the 2 keyframes you might have a state with all the morphs active.
For "solid animation" (so basically just matrixes in the graph that are animated) and rig/bones, the model is always deformed in the gpu.
It's important to keep the graph as minimal as possible, graph with many many nodes can be terrible for performances (hopefully we'll improve somedays).
However there's a limit of bones that you can use per geometry. It depends of the devices and we don't have fallback currently (so it will display a skeleton).
Typically the worst case is iOS with a limit ~35 bones.
The culprit is http://webglreport.com/ -> "Max Vertex Uniform Vectors", divide the number by 3 and you have an approximate of maximums bones per geometry.