The main risk is that another company can register an identical or confusingly similar trademark first. In first-to-file jurisdictions (the EU, UK, and most of the world), filing date determines who holds the rights. A third party that files before you can legitimately demand you stop using your own brand name.
The longer you wait, the worse it gets because bigger, more recognizable brands are also more attractive to copy. Rebranding an established business is significantly more expensive than registration would have been at the start.
In first-to-use jurisdictions like the US, prior commercial use offers some protection, but only in the geographic area where you can prove that use. A registered trademark holder in the same category can still block your expansion into markets where they filed first.