When you play at longer time controls, the odds even out a bit. Although a computer can do a deeper search in a game at tournament time controls, it's not deeper by a huge amount. Every ply you add to a computer's search exponentially increases the number of positions it must consider and each ply takes longer to consider than the last. It takes a computer longer to search just the eleventh ply alone than it did to search the first six or seven plies combined. We have more time to consider our options and to make those hazy long-term strategic plans that computers are incapable of devising.
Computers only see the short range possibilities.
Our abilities are the ones that change with the clock settings, not the computer's. Either way, the computer plays as tough as it can in the time you've allotted, so keep this in mind. It's very simple to set Fritz to play blitz or speed chess. You just set the length of time each player will have on his clock at the start of the game. This box is used for setting the increment for Fischer time controls.