Where it genuinely is not sufficient is your core identity. A logo assembled from library elements is not distinctive, may be used by other businesses, and typically cannot be registered as a trademark because you did not create the underlying components. Read the licensing terms carefully before building an identity from stock elements, because the restrictions on logo use are specific and are the thing most users never check. A logo is the one thing worth having made properly.
The second limitation is print production. Design tools aimed at general users handle screen colour well and physical printing less predictably, and colour that looks correct on your monitor can arrive noticeably different on a card or a sign. For anything printed at scale, have the printer confirm the file is suitable and supply the colour values in the system they use rather than assuming an export will translate.
The practical risk that catches people is dependency. Files created inside a hosted design tool live inside it, and if you stop subscribing or the terms change, your access to editable versions changes with them. Export the source of anything important to a format you can open elsewhere, and keep the finished assets in your own storage rather than relying on the platform as an archive.
Where it delivers most is consistency, which is the actual branding problem for a small business. Build templates for the formats you use repeatedly, with your colours and typefaces already set, and every subsequent graphic starts correct rather than being rebuilt from memory. That template library is worth more than any individual design and takes an afternoon to establish.
The honest summary is that the tool is not the constraint. A business producing poor material with it would produce poor material with anything, because the weakness is usually in deciding what to say rather than in the software. Spend the saved money on the logo and on photography, which are the two things that genuinely require somebody who does this professionally.
One workflow detail saves the most time later, which is building your templates around the exact brand values rather than approximations chosen by eye. Enter the hex codes rather than picking from a colour wheel, upload the actual typefaces rather than selecting something similar, and place the correct logo file in the template rather than one pulled from your website. Every graphic produced afterward inherits those decisions automatically, which is what turns the tool from something producing individual pieces into something producing a consistent brand.