One of NextGenSprites main Features is the ability to toggle Shader features at runtime. Let's say you let an Sprite appear by a dissolve effect. When the Animation has finished, your Sprite is fully visible, but the dissolve logic is still running on the GPU. This is why it is important to disable features you aren't using - just because we can't see it, it doesn't mean that it isn't there.
Via Script you can do it like this:
//some code happens here before mat.DisableKeyword(ShaderFeature.Dissolve.GetString());
Unlit and Single Lit are very fast, but Multi Lit can drain performance because the Shader has to Render a new Pass for each Point Light. When you are on Mobile, use the Multi Lit Shader very sparingly!