If an aggregate runs out of free space, various problems can result that range from loss of data to disabling a volume's guarantee. There are multiple ways to make more space in an aggregate.
All of the methods have various consequences. Prior to taking any action, you should read the relevant section in the documentation.
The following are some common ways to make space in an aggregate, in order of least to most consequences:
You can do this manually or with the autoshrink option of the autosize capability.
A volume with a guarantee type of none has a smaller footprint in the aggregate than a volume with a guarantee type of volume. The Volume Guarantee row of the volume show-footprint command output shows whether a volume is reserving a large amount of space in the aggregate due to its guarantee.