I noticed that when I install and uninstall applications slow down the phone and it is necessary to restart to restore normal function of the phone. Is it a case like a computer's, after installation should be restarted, and how Android resolves this case?!
Normaly it shouldn't restarted.
Nothing special or magic.
You did mention Apps2SD, that is where the slowdown is happening, more than likely, the filesystem on the SDCard is getting a bit fragmented (unless its non-FAT32 file-system from the old Windows 95 era). It might be better for you to use the Android's native filesystem (Ext3fs) to accomplish this.
You should not have to be restarting the handset in order to resolve it.
Question for you - what class is the SDCard you are referring to. Perhaps upgrading to Class 6 or better might help. (If you're bombarded by the terminology 'Class', its down to the speed of how fast the SDCard can be read in, generally, the higher it is, the faster it is, but then again that's depending on the SDCard slot if its capable of supporting it.)
You would be quite surprised as well, that maybe reformatting the SDCard can do the trick as well but if you happen to have apps on it.. that's definitely ruled out.