Why was this change important?
Google perceives URLs with and without trailing slashes as different addresses. This means that without the uniformity of having trailing slashes on all links, the search results for that a particular event (or any other form of content) now offer multiple ways for the site user to access that information. That's bad for SEO.
Let's use an event as an example. The best way to end up on the first page of a search result is to make sure Google notices that lots of people are checking out your event detail page. When people find the event through multiple different URL pathways, this dilutes Google's perceived demand to see that event, because it thinks it's actually multiple different events. This causes Google to push your page, as a search result, down the results list, to page 3 or 4 perhaps. When we use trailing slashes, this closes those other access points, and funnels all site users in through one proverbial 'door' to view the event, which boots Google's perception of the demand to see the event, and drives your event up the list of search results.
Think of it like restricting access to a hot nightclub. The demand to enter the building seems higher if people line up because they can only get in through one doorway. If there's multiple entrances, a line never forms and Google never fully understands the demand to get into your hot nightclub or...erm...your event detail page. You get the idea.