C#: What is the difference between Task and ValueTask?

1// Task
2public async Task<int> GetAsync() {
3    return await GetFromDb();
4}
5
6// ValueTask — better performance
7public async ValueTask<int> GetAsync() {
8    if (cache.TryGet("key", out int val)) {
9        return val;  // No allocation
10    }
11    return await GetFromDb();
12}