So I'm confused about the SP only bit. I've noticed there is some overlap with the sp only event, but is there a reason Broadmoor does a sp only? And I'm curious why a skater would opt to do both. I suppose it's a chance to get even more feedback and get in front of judges before the whole kit and caboodle.
I looked through the announcement and see that at this competition for events with elimination rounds, the initial rounds are freeskate-only and only the final round is short+free combined. So they advise skaters who want to make sure to get to compete their short program to enter the SP-only event.
That seems to be the main reason for its existence here. Skaters may have different reasons for entering it.
Different nonqualifying competitions set things up differently, so skaters may make different decisions at different events.
E.g., another reason to enter a SP-only event is to try out the higher level. Juveniles don't have short programs in qualifying competitions, so it's very common for skaters at that level to prepare and compete in the intermediate SP even though they have no intention of testing up to intermediate that year. (On the other hand, some competitions including Broadmoor Open do offer "Juvenile short program" as its own event, with the same rules as intermediate SP.)
Sometimes skaters compete at two different levels (current test level and one level above) during the summer to decide whether they want to test up before regionals or not. Broadmoor is one of the few that allows skaters to enter the same kind of event at two different levels, so a skater could test out both levels at the same competition. Otherwise they might need to try out the higher level at a different competition than where they compete at their current level.
At some other competitions, a SP-only event might be cheaper to enter than a combined event. So if a skater is only ready to compete the SP, it would make more sense to enter just that event and not pay for a freeskate that they have no intention of skating.
It really depends.