Removal, Briefly

"Removal is a spell or ability that is used to remove permanents from play" (MTG Salvation). Removal is a form of disruption. Unlike countermagic and discard, it can be used "after the fact" and unlike bounce, it's effects are permanent.

Many permanents have a huge effect on the game. A Grave Titan cannot be ignored. Olivia Voldaren or Jace, the Mind Sculptor will win a game given enough time. These cards are bombs; removal is the the anti-bomb. A Baneslayer Angel is extremely powerful, and so is the Doom Blade that takes her down.

To show up to a match without removal is to say you aren't concerned about your opponent's permanents. This is almost always a bad idea. No matter what your plan is, there will be permanents that will defeat you if not dealt with. Yes, bring your bombs, but bring your anti-bombs too.