the gc pressure is normally not so bad, but there is also more indirection in each iteration. So you iterate slower, and evict more data on your cpu caches. Whether this "matters" depends of course. Are you doing a ton of work in each step through the collection? If so, the overhead of linq will be small relative to that. How much do you care about wasting microseconds and eating more battery/power? At scale these little things add up, it can get important quick. On small devices it can be important. For a personal script running on a powerful desktop, it definitely doesn't matter, and everything in between.

My LinqFaster repo has some benchmarks showing time differences for some common operations in a fairly worst case scenario (where the work done in each iteration is small) https://github.com/jackmott/LinqFaster

It would just be nice if C# reliably compiled this abstraction down to efficient code, the way C++, Rust, and Java Streams do.