My first thought is: don't do this. If you have an application that requires multiple threads then that's fine. However consider that your computer's underlying architecture (processor) can only run so many threads at a time. The Operating System (OS) simulates multi-tasking by constantly switching which thread is executing at any given time. For example, if you have a simple single core processor, only one thread can be run on it at a time, so the OS will have to swap the currently executing thread if there is more than one. Of course, this over simplifies things and ignores all the other applications running on your computer, but that's the general idea of things.
If you have lots of tasks that can be threaded, consider using a thread pool (or using a library to do it for you) where you have a set number of threads that will run tasks from a queue.