There are a ton of discussions on the internet comparing these two lenses, I suggest searching around.
The 1.8 is popular because it is extremely cheap for a Canon lens. Personally, I thought the money I spent upgrading to 1.4 was well worth it. It’s much sharper wide open, the corners are sharper in general, and the better build and focus ring are worth the cost difference to me. Others are totally happy with the 1.8.
In general, primes (< 2.8 aperture) have a wider maximum aperture than zooms, which gathers more light in than zooms, allowing you to shoot in darker settings. That’s the primary reason people use them. In addition, primes are generally sharper than zooms, the difference is much more noticeable in lower end zooms. Whether this is worth it to you for profile and nature photography, I can’t say. I’m not sure what profile means, but if it’s portraiture then yes, IMO it’s worth it to have a prime.
