Formally, it depends on where you apply. In Norway, Mathematics HL is not a requirement, as Mathematics SL is considered equivalent to the highest level of high school math in the Norwegian system.
In Canada, Mathematics SL is accepted. I'm sure having Mathematics HL would be an advantage, though.
In the UK, Mathematics HL is a requirement for all engineering degrees I've seen, and for math, physics and economics degrees.
I'd reckon this is partly because Bachelor's degrees in Canada/US last 4 years, whilst in the UK they only last 3.
However, I know Norwegian students with R2 (the highest level of math in the Norwegian system) who have gotten into Engineering in the UK, which I cannot get into (due to having Math SL. Even though we learn the same as R2-kids), and they have done fine. So while it's definitely an advantage, I would reckon a better grade and more time for other tedious subjects is more valuable.
That said, I love Math, and had Mathematics HL for the first six months of IB, until my school decided to drop it because Mathematics SL gets us into everything here in Norway. A ridiculous decision, which means I now have to go to Canada to study, rather than the UK.
Hope I helped.