The only MCP server I use is Svelte's and every time I use it, I feel as though I'm just spamming my context window for little to no reason. I mostly only use it when I'm unsure about something.

However, it did feel useful when breaking changes were introduced, such as class->function component instantiation from Svelte 4 to Svelte 5.

This is probably true of any well-maintained MCP server provided for a project that has a rapidly-evolving API and highly opinionated maintainers who are unafraid to act on their opinions and break stuff. In that scenario, the Svelte MCP server seemed to act as a stop gap for context that the model's cutoff wouldn't allow it to have yet.