Avoid Using the "let" Keyword in LINQ Queries

LinqQueryPerformanceBenchmark.cs

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;

public class LinqQueryPerformanceBenchmark
{
    private List<Person> _peopleList;

    public LinqQueryPerformanceBenchmark()
    {
        _peopleList = new List<Person>();
        for (int index = 0; index < 10000; index++)
        {
            _peopleList.Add(new Person
            {
                FirstName = index % 2 == 0 ? "Admir" : "Tarik",
                LastName = index % 3 == 0 ? "Haris" : "Velid"
            });
        }
    }

    [Benchmark]
    public void FilterPeopleWithoutLet()
    {
        var filteredPeople = from person in _peopleList
            where person.LastName.Contains("Haris")
                  && person.FirstName.Equals("Admir")
            select person;
    }

    [Benchmark]
    public void FilterPeopleUsingLet()
    {
        var filteredPeople = from person in _peopleList
            let isLastNameHaris = person.LastName.Contains("Haris")
            let isFirstNameAdmir = person.FirstName.Equals("Admir")
            where isLastNameHaris && isFirstNameAdmir
            select person;
    }

    public class Person
    {
        public string FirstName { get; set; }
        public string LastName { get; set; }
    }
}

public class BenchmarkProgram
{
    public static void Main(string[] args)
    {
        var benchmarkSummary = BenchmarkRunner.Run<LinqQueryPerformanceBenchmark>();
    }
}

// * Summary *

BenchmarkDotNet v0.13.12, Windows 11 (10.0.22631.3737/23H2/2023Update/SunValley3)
AMD Ryzen 9 3900X, 1 CPU, 24 logical and 12 physical cores
.NET SDK 8.0.301
[Host] : .NET 8.0.6 (8.0.624.26715), X64 RyuJIT AVX2
DefaultJob : .NET 8.0.6 (8.0.624.26715), X64 RyuJIT AVX2

Method	Mean	Error	StdDev
FilterPeopleWithoutLet	10.62 ns	0.182 ns	0.152 ns
FilterPeopleUsingLet	76.97 ns	1.577 ns	1.817 ns

Method	Allocated
FilterPeopleWithoutLet	72 B
FilterPeopleUsingLet	360 B