To my point of view, It is a matter of accessibility to processes.
Before selecting the pid files directory, take a note of following points:
* Number of users accessing the machine(either from local or from remote).
* Access permission for the directory and pid file for other users. Because, the file can be removed/renamed/modified if it is accessi
ble to other users(knowingly or unknowingly). So, better to give permission which is enough.
* Different processes which could access the pid file (for inter-communication between processes (i.e). one process could read the pid file and send signal to your process).
Not noticing the above things, could create unnecessary problems sooner or later.