Thresholds are those that have a default value that cannot be exceeded unless the value is modified. Thresholds can, in certain circumstances, be exceeded to accommodate variances in your farm design, but it is important to understand that doing this may affect the performance of the farm in addition to the effective value of other limits. The default value of certain thresholds can only be exceeded up to an absolute maximum value. A good example is the document size limit. By default, the default document size threshold is set to 250MB, but can be changed to support the maximum boundary of 2GB.