Beasties are initiative in the bank. If your opponent has a monster, and you do not have a high-percentage way of neutralising that monster or killing your opponent, you are the one behind on initiative.
And of course, this means you need to protect that monster tenaciously. Most of the time, your defensive opponent, unable to respond as flexibly to the threat of dummying, will eventually open up some chink that allows you onto the attack, and once you're on the attack and you have a monster threatening two or more damage every turn, the game can be over remarkably quickly. Consider the consequences of each Charm and Maladroit that land -- these are now suddenly damage spells. Risking a P when charmed against a monster will leave you unable to stop Lightning without a horrid clap, and when you're so strongly on the attack you ought to push for damage unless your own position is very shaky.
Taliesin