The short answer
Restrictive covenants limit how a property can be used or altered, potentially preventing extensions, conversions, or changes of use.
A covenant attached to the title can quietly rule out the exact plans you had for a property, whether that's an extension, a loft conversion, or letting it out. They're easy to overlook because they sit in the legal title, not the listing.
Why this matters for your purchase
Restrictive covenants sit in the title review section of a PropM8 report, flagged before you've paid a solicitor to find the same thing weeks into conveyancing.