Lots of really interesting views, and a good balance for both sides.
In my experiences photo charters can be quite a good idea when focused - in one example the fees also paid for the engine to be repainted from LNER green to BR black especially for the charter- this was okay as it needed a repaint, but was also due its overhaul in a few years where we would need to paint it anyway, so black made a nice change for a while and we made money.
These charters used an intermediate station so people could get on and off the "period" stock safely and the train could then run back and forth. There was an out of the way stop where access was provided to get out, but as it had the whole line booked, and stewards to shepherd the photographers this was a safe operation (and there was a safety brief beforehand).
Photographers wanting the atmospheric evening shots of the engines relaxing on shed are understandable, but do get a bit in the way of the staff working to prepare them for the night, and this is about the only place I really see operational requirements at odds with the charter. That said, they do have to pay a premium for these sessions, and where possible every allowance is made.
However galas bring out loads of people with cameras - often very expensive which obviously leaves them no money to contribute towards the cost of the event as they either just stand on the platform or just outside the station. If you are on every train you tend to notice that they are always there and their bums never touch the seats.
As for the volunteers being bothered - few take pictures unless something special is on site apart from the younger members and those logging overhauls, and are quite focussed on the jobs they have. Many of the retired engineers just want to do something practical, and often had little interest in railways before they started here. Marine engineers in particular seemed interested in helping out with the steam engines - they cut their teeth on steam turbine engines and wanted to get back to their roots.
The non-enthusiast pool is vast, and if it offers something to people who previously just had the odd visit it can be a real bonus - many are very keen to learn new skills, or utilise those they have in new ways. I would love a couple of retired experienced spray painters to come along wanting to volunteer, and if they have only ever dealt with vans or trucks in the past that would not be a problem! On the contrary, it would probably be us looking to learn from them....