For the average hobbyist equipment calibration is not something that would be of any great importance. However, if you do commercial electronics it is usually a requirement that you have your test equipment professionally calibrated. This usually means your multimeter and other test and measurement equipment needs to be sent to a calibration facility on a regular basis. Usually once a year, give or take.
Different types of projects will demand different levels of calibration. However, this is an interesting topic. In my work experience I have often seen requirements that calibrated equipment be used for testing devices. However, tolerance is not always given in these requirements. A person could use a meter calibrated to within 50% and (I suppose) would meet the requirement, even though 50% is a laughable tolerance.
Costs will vary depending on the equipment being calibrated, level of precision, and turnaround time needed. For a simple multimeter (volt-ohm-amp) expect to pay around $50 for a simple calibration.
My usual experience with having calibration done on equipment involves sending a meter to a calibration lab. They usually send it back with a new sticker on it, but don’t make any adjustments. This is because modern meters are remarkably stable. Almost always the meters are still well within tolerance levels when I send them off for calibration, so they do not require any adjustment.
In the end the average ham radio operator, or amateur electronics hobbyist will not likely have a need to spend the money to have their equipment calibrated. However, it is not prohibitively expensive, and there is certainly value in knowing that your test equipment is giving accurate measurements.