Allocations are pretty cheap, but GC can be quite expensive under high load/big heap. It is probably not the first optimization you would need to make, but allocaitons have been a huge focus by the .net core team, and is part of the reason why it is so much faster than the .net full framework. See for example the post on improvements in dotnet 5: https://devblogs.microsoft.com/dotnet/performance-improvemen...
https://docs.microsoft.com/en-us/aspnet/core/performance/per... https://docs.microsoft.com/en-us/dotnet/standard/garbage-col...