At my uni, we make offers in terms of grades rather than points as boomting says. The extra UCAS points make no difference to the offers we make.
But when the exam results come out, they can make a difference. For example if an applicant has just missed their A level offer, but has additional UCAS points, this will be taken into consideration when deciding whether or not we will still allow them to come.
The reason for this is that university league tables often use average UCAS points as part of the method of ranking. So taking applicants with lower grades and additional points will have no impact on the league table, whereas taking applicants who just have lower grades will.
Using UCAS points in league tables is, of course, stupid. Universities can go up in the table by just increasing their standard grade offer rather than making any real change to the teaching quality. But they are made by outside agencies, so we have no control over this.
UCAS points are only really used by lower ranked unis, so they may or may not be relevant to your DD, and many unis will not accept the UCAS points from things like dance (or indeed, anything that isn't A Levels, BTECs, IB etc. They are a way of offering more flexible entry requirements (eg BBB / ABC / AAD / A*BD etc are all the same in UCAS points.
UMS are essentially a percentage score, and any scores within a certain range will be given a certain grade (eg 70-79 = B). Unis can use them to see whether they fell within the low / medium / high range of a grade boundary, but only the most competitive unis will actually bother.
Am I right in thinking that UCAS points are used to specify entry levels to university courses, but that UMS points are used to compare specific students? My DD is accumulating extra UCAS points through extracurricular activities (ballet and speech & drama), but once you have reached a certain threshold of UCAS points do these become fairly irrelevant, compared with UMS which is what really matters when it comes to university acceptances?