Risks of blocking loft hatch?
I think it's unwise to block access. There's a few reasons I can come up with, just off the top of my head.


if your roof is leaking, you need to get in there to see what the root of the leak is
electrical or plumbing upgrades frequently need attic access
if you get a creature problem, attic access is sometimes needed for trapping/mitigation
you might want to add insulation in the future
bath or kitchen fans might need replacement in the future


You can have a closet unit designed that allows access with a bit of disassembly.

If you don't want to go that route, a different hatch could be made, but there's carpentry and cost associated with that.