You don't have to use them, they're not necessity. Obviously it would be great if sampling algorithm could decide adaptively where to sample prioritively light (bidirectional sort of does) but it already does good job,
and portals often help best when the scenario is quite unique is size of the windows to room ratio being very small.
Also Corona's approach to portal light is simple and logical, it's just ray 'emitter', it does not become actual light source so you still get your realistic sun bouncing around without visual alteration, but you will get noise-free image faster.
I rarely use it (almost never) and I am doing just fine.