Advancing elements is moving their repetition to an earlier date. It is the opposite of Postpone.
Advance is helpful if you want to review topics in a specific short period (e.g. a week). It is also useful to make a thorough review of a subset of items, e.g. in case knowledge changes or portions of knowledge get damaged by forgetting.
In case of topics, elements will be rescheduled with new intervals falling into a selected range. For example, if you want to thoroughly review all topics related to whiplash injury over the period of two weeks, search for whiplash (Ctrl+F), choose Advance, and select 14 (number of days in the review period).
For items, Advance works differently. All items will be rescheduled within the period of the advance interval starting with tomorrow. Unlike in the case of topics, item intervals may still be very long. Just short enough to fall within the review period. For those items that are lucky to retain long intervals, if your recall is good, you will not need to waste time on reviewing them frequently after the review period. The formula for the next repetition date is the same for topics and items:
today+[1..Advance Interval]. The formula for the new interval is:
[1..AdvanceInterval] for topics and
(Today + [1..AdvanceInterval] - LastRepetition) for items.
Advance topics: If you specify the maximum interval as 100, all topics with longer interval will receive intervals randomly dispersed within the 1..100 range. Topics with intervals shorter than 100 will remain untouched. Advance topics executes mid-interval repetition on the affected topics (unlike Advance items).
Advance items: If you specify the maximum interval as 1000, all items with interval longer than 1000 will receive intervals randomly shortened so that to schedule a repetition between today or the day when the interval reaches 1000 days. All items repeated before 1000 days ago, will be scheduled for repetition today. Unlike Advance topics, Advance items shortens intervals without executing a mid-interval repetition (which would be illegal from the learning process standpoint as no repetition can be considered executed without you actually reviewing it).