A lot of old school bodybuilders used to crack open an amp of ammonia before hitting squats or the bench to give them a boost before hitting the rack to try and get a maximum benefit of the lift. However, further research has shown that smelling salts can be damaging neurologically and overuse can cause problem. Having said that, I'd like to try it just to see how it works and if you can keep them to a minimum (like when you're trying to hit more pounds or the last set you're doing) you'd probably be okay.
But, if you're doing it when you increase the weight, you can lift it and not feel the pain that could be from excessive weight. So, there are some pros and cons. You can still buy them online but I recommend limiting their usage
extremely.
en.wikipedia.org