Impossible to give absolute yes and no limits. Always open to interpretation. There will always be people in whatever position/profession who don't quite fit into the specific rules.
And as Tel says, one person's essential will be different to the next.
Totally get it, each job should be looked at individually and assessed. But consider some examples....
Plastering... required to keep things safe? Hardly
New carpets/flooring... required right now? Probably not
Finishing a kitchen... if it's things like putting doors on (i.e. the general finish), then that can wait but if it's finishing basic amenities like power, water and gas for cleaning, cooking, etc. that in my opinion is essential
These are some of the jobs I've put off...
Installing a new burglar alarm system - Not required right now, not safety critical
Moving some sockets and adding some - Not required right now, not safety critical
Installing power to a shed - Not required right now, not safety critical
Changing lights - Not required right now, not safety critical
Installing new outside lighting - Not required right now, not safety critical
So yes, common sense does have to come into play. The point I'm making is really about whether the guidance will be used to decide who can access the financial assistance for business.
As it stands the guidance allows me to continue working in peoples homes for undefined durations for any purpose and therefore in the eyes of government I can continue to run the business as normal. I'm choosing not to do that because in my opinion at this moment in time, it is the right thing to do for the benefit of everyone, but with the updated guidance that decision is not supported by government and as such it could prevent businesses from getting access to the assistance.