While a player is in free agency his price will fluctuate based on his play. And so, if a player in the open market goes on a 25 game hit streak and greatly balloons his previous value, should someone decide to pick him up they are going to have to pay that ballooned value. HOWEVER, having a player on your Triple A team freezes his price, no matter his production in the Majors, the day you added him to the Triple A roster. And so, that player whose value was ballooned by the 25 game hit streak (say his price went from $0.25 to $0.85) will remain stagnant on your Triple A team (remaining at $0.25).
This of course is a huge benefit for prospects with zero major league experience because you can have these players playing major roles on your team for free. Take, for instance, Jered Weaver in 2006. At times his price hit $4.00 (Albert Pujols is a $1.20) just because he started off his major league experience on a tear. Had Jered Weaver been sitting in Free Agency, should someone had wanted to pick him up they would have been grossly over-paying for his services. However, had a manager done a solid preseason scouting job and drafted him before he had any major league experience, that manager would be benefiting by his $4.00 value performances, for free. This is the value of freezing a player�s worth.