Allocation happens. You can leave it to the compiler, the runtime, or let the code control it.

The automatic solutions are usually pretty good and usually the right place to start. But if performance is a priority, you want options.

BTW, “per-frame arena” is part of a general pattern of a repeated interval of work doing significant allocation. This is really common in software of all kinds… servers that process requests (like web servers and database servers) and typical command line tools.