8 GB is not a lot of RAM for Ae. With this little RAM, things probably get a little sluggish because the system has to swap RAM.
In a low memory condition, the computer saves little chunks of used RAM to the hard drive, hoping they won't be needed right away, to free up the space in main memory for a more pressing need. When that virtual memory on the hard disk is requested, the computer has to swap something else out to hard disk to make space to restore the original memory from hard disk. RAM is very, very fast and hard drives are relatively slow, so this makes the system respond slowly.