In the old days (before the match) programs would simply offer a spot to an appllicant they wanted. The applicant would often take the spot, but would drop it later if a better offer came along. Then the program is left to send another invitation to fill the spot. This went on for months and it left some programs with positions vacant in the end, and applicants never new whether they should take an offer just so they can go somewhere, or if they should turn it down and wait for their #1 choice, which may not come along.
The match simulates this process with a computer algorithm that simulates the offering and accepting of positions, and it takes a few minutes and the results are given to everyone on the same day. There is usually a penalty for withdrawing from a program you matched in, such as not being allowed to go through the match for 2 more years. But this doesn't matter I guess if you go into another program "outside" the match.