You are correct. PLA is Polylactic acid. CF are fibres constituted mainly by carbon.
However, I am almost sure that none of us print pure PLA.
All materials have advantages and weaknesses, and different methods can be employed to overcome the latter. One example of polymers is the use of additives and reinforcements.
All filaments entail additives (pigmentation, surface(mate, silk, gloss), viscosity, etc.), representing a residual part of the composition.
It is possible to achieve more significant improvements by combining two or more chemically distinguishable materials. The new material is a composite.
For example, the PLA-CF composite entails a PLA matrix reinforced with carbon fibres. Some advantages and disadvantages of using CF are increased strength and stiffness at the expense of abrasive behaviour and clog prone.
The process is not limited to CF… other reinforcements and fillers are wood, glass fibre, metal powders, etc… (note: it may also be classified as composite hybrids, but it is pointless for the user).
Besides the material type, you can achieve completely different properties and challenges by using distinct ratios of materials. A simple example, at an aesthetic level, is wood. A typical PLA with up to 20% wood prints as PLA and provides a good wood look. An authentic look, surface and smell of wood can be achieved with PLA filled with a wood content of 40%. However, your house will smell like a woodshop, and clogs are often a nightmare of hours.
Regarding the use of PLA-CF as the central filament.
BL PLA-CF is extremely impressive at an aesthetic level. BL has some beautiful colours, but still limited. The other advantages (stiffness, strength, etc.) are minor compared to the aesthetic. The only downside worth mentioning is the cost.
I am waiting for the PETG-CF, so I cannot comment.
I mentioned BL filament because I have no experience with PLA-CF from other brands.
I mostly print functional stuff and use CF and GF composites with engineering-grade filaments (PA, PET, PC), but not daily. Not that I wouldn’t like to, but it is only worth using if there is a need.
My daily filaments are ASA and PETG, with some intercalation with PC and TPU. And PLA for other uses.
I found and read (in diagonal) this one some time ago and found it simple but interesting, as it isn’t limited to polymers and filaments: