References to RAM locations are explicitly tied to the processes that reference the location, when the process terminates, for whatever reason, the kernel will automatically refresh its "registry" that keeps track of RAM location references.
If a RAM location is not referenced by any running processes the memory in that location is "freed" and thus available when another process need to store something in RAM.
The RAM location is only occupied as long as a reference to it exist.
This has been the case for all normal OS's for time immemorial.
Real-time operating system (RTOS) are an exception to what I said here, but they are not normal OS's, no personal computers would have one of those.
Much software have memory leaks, also some of the typical processes that are always running on many computers, so it is not that rare to see a computer chugging more and more RAM the longer it has continually been powered on.
Sometimes a computer restart is the easiest way to deal with this, but as long as one have 2-3 GB or more free RAM, there is little reason to restart the comp. before launching C2C.
Back in the days when having only 512 MB of RAM was ordinary, or even when 4 GB was all one had, it was far from strange that a computer got all laggy and problemeatic after running for 2-4 days continually, especially for those who had many different processes running in the background all the time.
OS's can have memory leaks between version x and version y, and the same is true for graphics drivers, Motherboard software, fan controlling software, mp3 players, printer related processes, P2P clients, etc. stuff that often is running in the background.
The abundance of RAM in today's computer, like 16GB, makes this problem a very rarely noticeable issue.