Mixing it up randomly is better than playing like a total robot. But if you want to take it to the next level you should adjust your play by getting inside your opponents head. It is much more important to make adjustments to your play based on what your table image is than to
mix it up randomly.
Also mixing your game up at random can cause problems since your opponents may actually become harder to read once they see what you are doing. Therefore confusing both you and your opponents, and not just them.
Another reason is it has become such a common tactic to now days. It may work on the new guy but a good player can actually anticipate someone is going to change gears in poker.
Realize that the poker books that recommend this play are twenty years old or more. And outdated since most decent players you would be trying to fool have either read or heard of this tactic. And it doesn't work on the bad players either. Since they don't know how to play, don't care or are not paying attention.
Most of these books recommend playing loose preflop then tight and back and forth. This is good but again, changing gears at random is not the best tactic. Switching from loose to tight by getting into your opponents head and then adjusting is much more effective. At least against opponents that are paying attention. For when and how to adjust see the page on Adjusting Play.