Braided fishing lines have become very popular during the past few years.  They work well in certain fishing situations and are extremely strong.  They do have some drawbacks that out weigh the benefits at times, though.

Braids are made by braiding or weaving fibers of a man-made material like Spectra or Micro-Dyneema into a strand of line.  This makes a very strong, tough line that is very abrasion resistant.  This line is so strong that you have trouble breaking it when you get hung up.  A fish is very unlikely to break it.

Braids are very visible in the water.  For that reason many fishermen do not like it in clear water. It may spook the fish, especially on finesse baits where you are trying to entice a fish to bite a lure they can see for a long time.  

Some folks say braids will cut into rod guides on inexpensive guides.  If you use it you should make sure your rod can handle it.

Braids have a small diameter, are very limp and don't have any memory.  They float so they can be good for topwater baits, but they have very little stretch so it is possible to pull the bait away from a fish.  And you must  have drag set so a fish does not rip the hooks out of its mouth if it makes a strong run right at the boat.  You can even break your rod because of the lack of stretch if you set the hook too hard.

Cutting braids can be tough.  Most fishermen that use them carry scissors to cut them since clippers don't work very well.

Braids are good in many applications but not good for everything.  Give them a try but be aware of their drawbacks.