But Whippy, I think you've really only argued my point for me. As a controller, the weather conditions are largely immaterial - an IFR approach is an IFR approach even if it's a lovely sunny day.
You're quite right that any pilot that elects to operate IFR should receive the appropriate service. But if there are two in the hold doing practice approaches and go-arounds below a 'real' IFR approach (no offence intended) how does an expected approach time in, say, 60 minutes suit. If there's only one beacon there are few easy (or, more importantly, quick) ways of getting the trainers out of the way of the 'real' IFR aircraft.
And bear in mind that although you'll always keep a level clear for a go-around, when an aircraft does go-around it will often further limit the available options and extend EATs. Therefore, by booking training flights, the airport is ensuring that ad-hoc arrivals get the appropriate service while accommodating a level of training that can be handled in a sensible manner.
My apologies to Fuji and colleagues for what might appear to be becomming a discourse on ATC procedures. I hope if people have taken the time to read this far it's because it's interesting.
From a personal perspective, I recognise that everyone has to learn and practice their skills and I'll try and make sure that delays are as short as possible. Yes, I'll accept six aircraft for instrument training, but four will simply go round the hold. Without wishing to start a debate about traing schools, your school may be happy to take money off you to fly round the hold but is that good value if you've got holds sorted and want to practice approaches?