When gaming and you have those times when the game has an intense exposions or large scenery or a lot of characters the demand for more processing power will cause the turbo boost to kick in and supply more power for the game to use. So yes it's a very good thing.
I am Alaukik and i want to know that turbo boost is good for gaming purpose.
My specs are as follows:
intel i5 2450M (2.5Ghz) but has a oost upto (3.10Ghz) and HD Radeon 7650M 2GB graphic card.
I'm not an Intel expert, but I've looked into leaving something similar the "Core Performance Boost" on in my AMD. I've heard when you leave it on, not all of your core's will run at the highest clock speed, it will only run one core at that turbo clocked speed. You might want to look into this further for a definite answer or watch YouTube videos with people overclocking your exact i5 model. Like I said I'm running on AMD with a completely different architecture, I just want you to get the most out of your CPU.
But I do agree with the above two comment's, as far as Intel goes, from what I've read the turbo mode on those CPU's are wicked for gaming. If your system is already running great with it on then leave it on, only if you are trying to push it past the limit at 4Ghz you might want to look at shutting it.
The issue with the computer that Alaukik_31 has is that it's a laptop and as such the adjustments are not many and certianly not like a desktop. In my bios when I go in there I can set the boost to either one core or all cores or disable it.