_Results.md

BenchmarkDotNet=v0.12.1, OS=Windows 10.0.19041.450 (2004/?/20H1)
Intel Core i5-4258U CPU 2.40GHz (Haswell), 1 CPU, 4 logical and 2 physical cores
.NET Core SDK=5.0.100-preview.5.20279.10
  [Host]     : .NET Core 3.1.7 (CoreCLR 4.700.20.36602, CoreFX 4.700.20.37001), X64 RyuJIT
  DefaultJob : .NET Core 3.1.7 (CoreCLR 4.700.20.36602, CoreFX 4.700.20.37001), X64 RyuJIT

Method	Depth	Mean	Error	StdDev	Ratio	Gen 0	Gen 1	Gen 2	Allocated
StringConcatEnumerableRepeat	0	16.710 ns	0.0743 ns	0.0695 ns	1.00	-	-	-	-
NewString	0	2.660 ns	0.0484 ns	0.0429 ns	0.16	-	-	-	-
StringConcatEnumerableRepeat	1	42.820 ns	0.3366 ns	0.2984 ns	1.00	0.0255	-	-	40 B
NewString	1	9.185 ns	0.0985 ns	0.0921 ns	0.21	0.0153	-	-	24 B
StringConcatEnumerableRepeat	2	88.547 ns	1.7138 ns	1.4311 ns	1.00	0.0457	-	-	72 B
NewString	2	9.807 ns	0.0920 ns	0.0816 ns	0.11	0.0204	-	-	32 B
StringConcatEnumerableRepeat	4	103.794 ns	0.5806 ns	0.5431 ns	1.00	0.0457	-	-	72 B
NewString	4	10.290 ns	0.1617 ns	0.1350 ns	0.10	0.0204	-	-	32 B
StringConcatEnumerableRepeat	8	145.738 ns	0.6164 ns	0.5766 ns	1.00	0.0508	-	-	80 B
NewString	8	12.237 ns	0.0952 ns	0.0795 ns	0.08	0.0255	-	-	40 B

Program.cs

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;
using System.Collections.Generic;
using System.Linq;

class Program
{
    static void Main(string[] args)
    {
        BenchmarkRunner.Run<Tests>();
    }
}

[MemoryDiagnoser]
public class Tests
{
    [Params(0, 1, 2, 4, 8)]
    public int Depth { get; set; }

    [Benchmark(Baseline = true)]
    public string StringConcatEnumerableRepeat() =>
        string.Concat(Enumerable.Repeat(" ", Depth));

    [Benchmark]
    public string NewString() =>
        new string(' ', Depth);
}