Time was, a machinist could find everything he or she needed for cutting advice in the Machinery's Handbook, the one book (aside from Machining For Dummies) that all individuals involved in machining should have in their toolboxes, on their desks, or in their nightstand drawers.
There's still loads of good feed, speed, and DOC (depth of cut) information in "The Bible," as it's called, but the pace of change in cutting tools has ramped up substantially in recent years, and the best source of such information in most cases is from the suppliers themselves. They're the ones that employ countless elves who work in secret chambers deep underground developing and testing new grades, geometries, and coatings. When they think they have a home run, they release their latest brainchild on the machining community, along with some darned good advice on how to get the best performance from it.
Of course, if everyone just did what the salesperson told him to do or bought what he was told to buy, every shop would be the same. Where would be the competitive edge? That's why you should always follow the cutting tool provider's recommendations until a stable process has been developed, and then set aside what you've been told and start playing.
It's okay; you won't hurt anyone's feelings. Sales people have thick skins — they wouldn't last very long otherwise. You can even invite them to stay while you go all "mad scientist" on your metal removal processes. The point here is to push the tools hard — even to the point of breaking — and then back off just a bit.
Don't do it willy-nilly. Testing any new technology must be done scientifically. Document each small parameter change and record the results. Keep track of tool life and surface finish, what toolholders were used, how the workpiece was held, what the machine sounded like, and all the other minutiae that machinists sometimes take for granted.
And if things go in the toilet (as they often do), you shouldn't just assume it's best to slow the tool down. Sometimes the best way to kill chatter or get past a little built-up-edge (BUE) is to push past it. Kick up the feed rate by 10 percent. Try a little more rpm. Swap grades and start over. Granted, all this testing consumes valuable machine hours. It must be done prudently. If the parts are due on Friday, now is not the time to start testing the latest multiphase coating. But test you must if you're to gain the upper hand. And remember: document, document, document.
The premise of "be all that you can be" in metalworking should be taken with a grain of salt. Why spend an hour fine-tuning a machining process if the job only takes two hours to complete? Why look for a tool that provides 10 percent greater tool life in Inconel (or spend extra money for one) if there's no chance of the job coming back. As long as you're getting acceptable tool life, good part quality, and can predict when the tool is going to fail, there's no reason to look for a super-tool, certainly not on the short run, high mix work common in many shops. In these cases, a good quality, general purpose tool is often the best bet (that is, unless the shop is slow and you have nothing better to do than test cutting tools). Innovation is a balancing act between necessity, logic, and the drive to make processes more efficient. Choose wisely.