Pros: can do a lot of things
Cons: doesn't do everything
Imagine you just bought a new racquet but now you decide that it would be perfect if you could just tweak one thing about it. Let's say you want it to be a little more stable so your stick won't twist when you're playing big hitters. What do you do?
If you answered, "Get a new racquet!", think again. Many problems (too much power, too little control, not enough spin, etc.) can be fixed by tinkering with different strings strung at different tensions. If your racquet isn't stable enough or isn't heavy enough for you, or if the sweetspot is lower or higher than you would like, or you'd like to get some more power, you can save yourself a lot of cash by experimenting with lead tape first.
Lead tape is just that...lead with an adhesive backing so you can stick in onto your racquet. Usually people put lead on the inside hoop of the stick, on both sides of the grommets. To do this, you usually have to cut the lead tape into 1/4 inch wide strips, so I recommend getting 1/4 inch wide lead tape so you don't have to go through the hassle of cutting 1/2 inch lead tape in half. Of course, putting lead just on the head of your racquet can alter its balance, so you probably want to put some lead on your handle (under the grip) or inside your handle. Most sticks' butt caps pop out with a screwdriver and you can put some lead tape in there. Heck, put it right on the butt cap! Once you decide on a set-up that's right for you, you can put fishing weights in the cap and surround it with cotton so it doesn't come out as a lot of people do. I just leave it under the grip.
One important thing to keep in mind is one should add lead in small amounts, play with the racquet, and then add more weight if necessary. Another is to have a goal in mind. If you think of the racquet face as a clock...
Add lead to the 12 o' clock position for more power. Because torque = mass x distance (or something), even a small amount of lead here can make your racquet swing a LOT heavier. The good news is that this setup will give you some extra juice on your shots...if you can handle the weight. It will also move the sweetspot of your racquet up. The problem is that not many people can handle much weight at 12. I tried it on my old Pro Staff and it felt much too sluggish for my liking. Rafael Nadal adds lead here.
Or add lead to the 10+2 positions for more power without as drastic of an increase to heft. Weight there will also move the sweetspot of your racquet up a bit...this is a staple of Prince's "Triple Threat" technology. So next time you mis-hit a ball, notice where you're mis-hitting it. If you're hitting a lot of balls near the top of your frame, some lead at 10+2 can move that sweetspot on up for you. A lot of modern racquets have sweetspots in the upper portion of the racquet face anyhow though. Pro Staff racquets have sweetspots that are slightly below center...
Or add lead to 3+9, like I did. This keeps the sweetspot in the middle and doesn't add too much heft. But you do get some more power and the racquet becomes much more stable. This is the most common place to put lead. Pete Sampras used an incredible amount of lead here.
5+7 will move the sweetspot down and give you some extra heft/power, but not as drastically as the other options.
Lead at 6 will increase the weight of your racquet with minimal difference to the swingweight.
And adding lead at the handle can make your racquet more head-light (just as adding lead anywhere on the head makes it more head-heavy) without adding much heft at all.
The thing to keep in mind with lead is to experiment with small amounts and first and try different things until you find something that works for you. This can be an endless process unless you have a clear goal in mind. For example, I wanted my Head Flexpoint Radical Tour to be more stable, feel heavier, and add some juice to my shots. A few strips at 3+9+handle did the job nicely.
However, lead has its limitations. First of all, some sticks just don't seem to take to lead as well as some other ones do. Second, you can't completely change a racquet into something it's not. For example, you're not going to want to turn a 9 ounce racquet into a 12 ouncer...all that lead is just going to make your racquet feel dead.
So yeah, sometimes you need a new racquet. BUT if your racquet is pretty good and would be great if you could change one thing about it...try some lead tape.
All lead tapes are the same thing except Babolat which has Babolat written all over it. The Unique and the Gamma ones seem to smudge a bit so make sure you wash your hands when you're done putting this on your racquet. You don't want to eat lead.
In conclusion, lead tape can do a lot of things and is worth $3 or so to experiment BUT it's not a miracle worker. Also if you want to make your racquet LIGHTER then lead isn't really going to help you.
Hey, if you have the time, check out my tennis stick buying guide.
I currently use the Head Flexpoint Radical Tour and Signum Pro Poly Plasma 17 @ 56 lbs.