It's really a question of how important it is to you. That said, if you live in an apartment and do not have a medical license to grow there, I can't imagine not having one. Imagine the cost of getting evicted versus the $50 dollars it costs to build a DIY filter.
I built a carbon filter out of contractor's cloth, carbon air filters, fish tank carbon, duct tape, and a fan I already owned. I can literally smoke a cigarette 5 feet away from my girlfriend in the same room and she can't smell it if I blow oke into the filter. Cheap and easy. Always worth it in an apartment.