Overstacking can be very dangerous against an aggressive opponent. If a player is not able to get down to the garbage efficiently, he'll be overwhelmed by garbage.
Fundamental
In this situation, a player overstacks and takes longer to get down to the garbage.
With the same sequence of pieces, a player can opt to switch the position of the T and the J, resulting in a clean opening for the garbage.
Towering
When facing an ever changing system of garbage, often, a player has to make the field uneven in height to avoid overstacking.
Be wary when towering because it's not always productive. If a player is not careful, he may end up severely decreasing his options in tetromino placement.
Sometimes a bit of planning based on the piece preview may help:
Foresight
When a player is confronted by diverging garbage columns, remember to also stack low in the column where the lower empty column resides. Don't always chase after the nearest empty column and cover the path to the next column.
In this diagram scenario, a player has to take an extra step in clearing a single towards the end.
With the same sequence of pieces, the player can spend less time in reaching the lower empty column.
