Another new feature of the later versions is a sampling profiler - in this mode the overhead of the profiler is low enough that it can be considered to be effectively nonexistent in most cases.
In the instrumentation modes, which capture the most detail, there's effectively no way to turn the profiler on or off: once the JIT has done its work, the instrumentation is in place and can't be changed. Additionally, the profiler would still need to track program state even when it was not measuring timings, which means the main effect of having an 'on/off' switch would be to make the profiler run slower (with the switch in either state). The best way to improve performance is to turn down the amount of instrumentation that is performed - in particular, line-level timings can require a lot of processor time to deal with.
Most profilers have an on/off switch in any case to make it possible to limit the final results to a specific time period. ANTS doesn't need this because it has the timeline and the ability to return profiler results for any time period by dragging out a region, so it's possible to just ignore the results from uninteresting times and easy to look at many different areas of the program in a single run.
This is particularly aimed at applications with long setup times: it means that it's not possible to make a mistake that would result in the interesting part of the data being lost, and also makes it easy to take a peek at the early data to ensure that the profiler is indeed capturing what's required.
Red Gate Software Ltd.