Ask HN: What is seed funding mostly used for in startups?

Founder living expenses.

It pays your founders life expenses. It usually last 6 months so they can build their MVP, get some initial traction and go after a larger round without starving.

Generally employees' salaries are the biggest expense in almost every startup and at every stage. Hence the saying that "overhead walks on two feet"

I've done quite a bit of initial patent work for startups that paid me with seed funding. Its important to get your patent applications filed early, so you can exclude your competitors from entering into your space.