I did an EPQ this year so here we go,
If you have a specific degree in mind and you want to write an EPQ relating to it, plus you think you can find the time to properly do it then it's worth it (imo). Some universities will give you a reduced offer if you achieve a certain grade in the EPQ, plus you can talk about it in your personal statement.
However, it takes a considerable amount of time. Lots of people dropped out of it in my classes. You also have to realise its not just the dissertation/report, you also have to complete evaluations, source evaluations, a log of what you do each week, referencing and do a presentation. My college did it from September till April.
It doesn't have to be related to what you wanna do but imo it'll only really be useful and worth it if it related