Signed distance fields only work well for relatively simple graphics.
If you have highly detailed characters like Chinese or emojis, you need larger resolution to faithfully represent every detail. The problem is that SDFs are sampled uniformly over the pixel grid. If the character is locally complex, a high resolution is required to display it, but if the character has simple flat regions, memory is wasted. One way to get around excessive memory requirements is to store the characters in their default vector forms and only render the subset of required characters on demand, but then you might as well render them at the required pixel resolution and do away with the additional complexity of SDF rendering.
If you have highly detailed characters like Chinese or emojis, you need larger resolution to faithfully represent every detail. The problem is that SDFs are sampled uniformly over the pixel grid. If the character is locally complex, a high resolution is required to display it, but if the character has simple flat regions, memory is wasted. One way to get around excessive memory requirements is to store the characters in their default vector forms and only render the subset of required characters on demand, but then you might as well render them at the required pixel resolution and do away with the additional complexity of SDF rendering.
SDFs are still useful though if you have to render graphics at many different resolutions, for example on signs in computer games, as seen in the original Valve paper https://steamcdn-a.akamaihd.net/apps/valve/2007/SIGGRAPH2007...