Vet keeping dog for many hours at a time

I have a cocker spaniel that is 14 years old, and relatively healthy.   He has some ear issues, and allergies so he's taking Apoquel and has ear cream.    For some reason, our vet likes to keep the dog for 6-8 hours at a time, just for regular checkups.   Yesterday, he had a scheduled appointment for 12pm , and was ready to be picked up around 7pm -    Aside from having surgery, or some other life threatening situation, is this normal at all?!    Is there a reasonable circumstance where a vet would keep an elderly dog (in a cage i assume) for this long, other than to rack up charges?!    Thank you for any input :)

Hello - yes, there are other reasons we might keep a dog in for a long time.  These include fluids, which need to go in slowly, sedatives which are needed for some procedures, and sometimes just to get enough staff together in a busy clinic to carry out a proceedure.  I have certainly kept dogs in to insert certain ear treatments because I have needed more than one nurse around to help to keep the patient still and calm, or someone experienced to observe the procedure / hold things and pass them to me in the right order, for example.  What interests me here is that there has been a breakdown in communication - if the information that you need is not offered, it is perfectly alright to ask why something is done in that way.   'Can you explain to me why my dog needs to stay in all day for this procedure?' is a perfectly reasonable question.  As is, 'Will they be in a cage?'  Some vets have cages, but many have walk-in kennels, such as dogs are sometimes kept in when their owners go on holiday.   There may often be a kennel nurse on duty to look after them.  I hope that you get to the bottom of this.