I've been a huge fan of using addies for working out for years now. Although I have been legitimately diagnosed with ADD, the doctor would write me a script for 30mg XR pills. I personally prefer the IR pills as my schedule can be inconsistent and even when you think the XR's have run their course, they sneak up on you again which has led to many sleepless nights.
For me, 15 mg IR about 15 min before the gym works great. Sometimes a chew them if I'm looking for a more "upper" sensation. Again, just speaking for myself, but I personally have never liked, and in some cases, haven't even been able to handle certain stimulants. Clen, Albuterol, Yohimbine, any over the counter weight loss pill or pre-workout, ephedrine, basically I don't really tolerate anything found in stimulants other than beta-alanine. However, Adderall has never caused those jittery, speedy, anxiety inducing effects (unless I mix it with something else such as caffeine). I've found that it helps keep me motivated in the gym and gives me the drive to complete every set of every exercise. Often it leads to me resting significantly less between sets without even realizing it.
However, the flip side is that sometimes instead of being focused on the workout and being mentally present for each rep, I start to think about other things I could get done or that I may have to do and it can lead to me rushing through workouts to an extent (although in all honesty, this is not that common and when it does happen, I still feel like I get a better workout in). Another downside is that adderall constricts blood vessels making it harder to obtain a good pump. They also make you sweat like crazy which isn't necessarily a bad thing, but that is a definite side effect.
From my experience, Adderalls work great for cardio and for higher volume workouts with less rest between sets. They are also good for dieting, although, unfortunately this can hurt your gains if you're looking to put on size as it can really kill your appetite. If you do choose to pop addies for your workouts, I would just suggest that you be careful not to become dependent on them. Don't take them before every workout, try not to increase the dosage once you've found the right one, and if you use them for other aspects of your life, keep in mind that they can build up in your system. Also, I think they can lower your testosterone. Just my personal experience anyway.