With digital photography so easy and cheap, I certainly use my
camera to keep a record when I'm researching a novel. I not only
photograph the scene from various angles so I can better describe
whatever aspects I might need to when I come to write, but I'll
also take close-ups of name signs for roads, or buildings, dates
carved in stone lintels, brass plates that list building occupants
etc. Where there is a tourist display cabinet with a poster-sized
page of written data, I'll snap that and, suitable enlarged, I have
an instant permanent record of all that information.
Remember, where appropriate, to try to include a suitable object or
person in a scene that will give you a sense of scale later when
you're using the photo and want to say, 'He reached up and plucked
an apple from a low branch', when in fact the old orchard only has
mature trees that need a ladder to get at the fruit.
I even use my camer to record a short video sequence of someone
talking or, maybe buskers playing in the street, although I do use
a tiny digital recorder for longer interviews - to save taking
notes. I've even used that clandestinely in my pocket while
chatting to some hardline republicans on the Falls Road in Belfast
(probably illegal, but it was only to use as an aide memoire). I
don't expect they would have been too happy if they'd seen it

.
But I'm going off topic. In a similar vein, and to come back on - a
good zoom lens is great if you want to snap something going on at a
distance without drawing attention to yoursef and your interrest in
what's happening. If necessary you can have a friend pose for you
in the foreground so the shot appears innocent, but direct and
focus the lens on the distant scene over their shoulder. I did that
in Egypt where it is illegal to photograph police, who look more
like members of an SAS swot team - they do really, I have the photo
to prove it

.