Remember that if you receive ANY consideration, both monetary or otherwise, for an aerial operation, you will need to have a PfCO and commercial insurance. So even for a 'small project', if you receive any consideration for undertaking it and you don't have a PfCO and insurance, you will be no better than the hobby pilot taking a job off a legal operator and breaking the (admittedly so far un-policed) law.
It's a feather in your cap having a PfCO. Certain parts of the regulations covering drone use are relaxed and you are able to fly legally in places that the hobby flyer legally can't. For example, the 150m rule for flying in a congested area is relaxed to just 50m, but the costs involved are overwhelming unless you can get paying jobs at realistic rates to cover those expenses. So you must ask yourself: 'Is it worth the initial thousands of pounds it will cost for the legal privilege of being able to fly 100m closer to that group of houses?'.
A small note: You are not guaranteed the be granted a PfCO by the CAA. That is a given. However, when I first went the PfCO route the instances of people being refused a PfCO were not very common. Often, after a first refusal, people were able to get one granted by a simple re-working their Operations Manual to get a successful assessment of it. But as time has moved on those refusals are becoming more common as the CAA is becoming stricter. I have heard that some pilots have been refused repeatedly and each refusal will cost money.
My advise to anyone reading this is to think long and hard...and make sure you have very deep pockets.