I really wish the anti-caffeine meme on the internet would die. While it is true that the alertness/wakefulness benefits are greatly reduced with habituation, caffeine has a whole host of benefits:

1. It helps promote a healthy body weight by suppressing appetite and boosting your metabolism.

2. It enhances dopamine action in the brain which is linked to improvements in learning and memory.

3. It has been shown to be neuroprotective; caffeine consumption has been linked to lower rates of both parkinson's and alzheimer's.

4. Caffeine intake has even been linked to higher testosterone levels.

So, enjoy caffeine all you want, just don't consume so much you feel overstimulated, or can't get to sleep at your usual bedtime.

I only have my own experience to go on, but I feel considerable benefits from giving up caffeine completely (about 6 years now). I feel mentally broader, calmer, less pointy. That being said, I do miss the smell and taste, and the buzz :)

What is limited caffeine? I see/hear this a lot recently, how much caffeine impacts our sleep cycle. I have 2-3 caffeinated beverages a day (usually 1 dark coffee and 1-2 cups of tea), but wonder if even that limited amount is impacting my sleep cycle.

I think it depends on your height and bodyweight, tolerance, and how quickly you metabolize caffeine. You also should be counting total mg of caffeine ingested.

I metabolize caffeine slowly and have practically no tolerance. A medium-sized latte anytime after 5 PM will keep me up all night. A decaf equivalent will make it really hard to fall asleep (remember that decaf still has caffeine).

I think my limit when not ingesting caffeine in the early morning is about 200mg before I have issues with falling asleep.

I think the optimal quantity of caffeine varies from person to person and would be affected by individual tolerance and biochemistry.

I've seen research suggesting the use of repeated low dosages (20-200mg per hour) throughout the morning and early afternoon for optimal performance. However, many of these studies have very small sample sizes and should be read cautiously.

I feel best with no caffeine at all.

I'm familiar with the evidence for all your claims except for the one about caffeine.

Why limited caffeine?

What I've seen is that caffeine works for some people and it doesn't work for others.

Caffeine may be functionally useful for some people due to their schedule, but any biological benefits would be outweighed by negative side effects if consumed too much(hence limited). Someone who is getting a healthy amount of sleep, eating properly, exercising and also at a healthy weight wouldn't benefit much from a lot of caffeine anyway.