In reply to Stuart (aka brt):
It's the installer that benefits - from the extra work. For the minor things you get the work done and pay it back via the saving to your electricity/gas bill. It's based on theoretical saving - so if you don't make that saving you'll have a net cost each year. The installers doing the work are always expensive, and not necessarily the best - the good installers tend to have enough work anyway.
I had to have a green deal assessment (and new EPC) just after buying our house last year in order to get RHI and FiT payments for 3 new systems I put in (ashp, solar them and solar pv). The green deal is copulsory for this, and was a waste of time, but the assessor knew that - she did both at the same time, the EPC is also pointless - but for another reason. The green deal only makes sense if you, for example, don't have double glazing and couldn't possibly afford to buy it from a reputable supplier the normal way.
Also, watch out for unscrupulous installers finding other "problems" when they do any "free" work.