Why does project save slow down over duration of project life?

Question

I notice when I'm editing in a project in Premiere Pro CC, the auto save or even if I just save, the save slows down over time. You can slowly see the save bar going slower and slower over time.  Even if I don't add any new media or import different files the save still goes a lot slower overtime. Sometimes the save bar will hang at a certain point for 20 secs or so and then continue. I understand if I add more media, files, pics, music etc... the save will take longer. But why does it do this if I'm just editing with some effects? Is it something to do with the cache folder getting too large or that I have too many auto saves? Should I clean out these folders? Also if it hangs at one spot for 10 secs or so is it because there is a corrupt file somewhere?
I just find this very frustrating if you are saving every 5 mins and you have to wait for 30 secs for a save.
My specs: Mac Pro 2009
Processor  2 x 2.26 GHz Quad-Core Intel Xeon
Memory  32 GB 1066 MHz DDR3 ECC
Graphics  NVIDIA GeForce GTX 680 2048 MB
Startup disk SSD

Answer 1

I can answer some parts:
The auto save works as a five project silo.  Once the list gets to 5 saves, it starts to write over.  Also the auto-save only saves the project--no assets, no renders, thus the file is relatively small.
applying aneffect (filters transitions, etc) causes the program to create a new file as Premiere does not modfy the original asset.  The more effects that are used, the more files that are created.  When you finally export, the AME creates a single file, once again, not affecting the original assets.