The 27mm pancake is the first XF lens I got when I made the transition from X100S to X-T1. The reasons were twofold- the cost and the size. It is by far the most affordable XF lens and when it is attached to the camera body, it is not much bigger than a body cap, and it actually fits into the pocket of my winter parka. The compactness makes it ideal for street and candid photography or whenever you need to sneak up on a cat (more on that later).
It is the most underrated and the least mentioned lens in the XF prime line-up. It has been given the middle child treatment. It is not a specialist like the 14mm or 56mm or a jack of all trades like the 23mm, nor is it a master of bokeh like the 35mm. While I would agree with all of the above, as a compact and lightweight option, the 27mm more than holds its own in terms of image quality and sharpness at f5.6 and up, and I find its autofocus speed to be one of the fastest amongst the Fuji Prime lenses. The build quality is more comparable to the lighter weight XF 18mm and XF 35mm, and not as solid as the 14mm, 23mm, and 56mm, which are bigger and more hefty.
Another added bonus for me personally is that it allows me to get close to my cats. Cats are my favourite models, the problem is they usually run off when I stick a portrait lens in their face, but with the 27mm, they seem to be at ease and natural in front of the camera. Below are a couple of examples:
All in all, the 27mm deserves some props for being an excellent walk around lens with great image quality and portability. For me, it was a great introductory lens to the XF prime line-up due to its affordability, and together with the other two lightweight XF lenses, the 18mm and the 35mm, they form a very solid trio that will win over the hearts of many street photographers.