The File->Configure->Smart Beaconing dialog

This dialog box allows you to set parameters for the SmartBeaconing algorithm.

SmartBeaconing™ is a beaconing algorithm invented by Tony Arnerich KD7TA and Steve Bragg KA9MVA. It adjusts your beacon rate based on your station's actual movement instead of just beaconing at fixed intervals.

Used appropriately, this algorithm can provide more accurate reporting of your track than the standard "just transmit every few minutes" method would. Used appropriately, it can do so with fewer position reports than the standard, because it is designed to beacon most frequently when your course and speed are changing a lot, and less frequently when you are just moving in a straight line at constant speed. It also adjusts your beacon rate based on your speed (higher beacon rate when you're moving faster, lower rate when you're going slow), because there's no point in beaconing every 3 minutes if you've only walked at 3 miles per hour (going less than 800 feet) during that time.

It has a lot of parameters, and it is easy to set these parameters in such a way that you spam your local APRS channel. (KM5VY has personally witnessed stations using SmartBeaconing with badly chosen parameters transmitting every 5 seconds for an entire traverse of the state of New Mexico --- effectively jamming the APRS channel for several hours.)

Xastir has added an additional parameter, "Wait Time" to the standard set of SmartBeaconing parameters. Xastir will not transmit more often than the wait time, irrespective of what the SmartBeaconing algorithm tells it it should.

Consult a good reference on the proper way to adjust SmartBeaconing parameters, such as https://qth.app/QTHHelp/English.lproj/adv-smartbeaconing.html

The standard parameters on that site are good options.

Unfortunately, many web pages on the SmartBeaconing algorithm direct you to a site "hamhud.net" that was the original source of the algorithm. This site is gone and has been captured by a gambling site.