In reply to Jeff Chandler.

If you have lots of images uploaded, then they take up space in the database, as they are attachments. Large databases, particularly those with lots of data in a single table, are slower than those containing less data.

This makes logical sense, since if there is less data to sort through, you should be able to find it faster.

@Bob, it is unlikely that you will need to worry about the number of attachments you have, unless it is a truly enormous number. In that situation, you could work around this issue by uploading the images, but not attaching them. I've never worked on a project where this was necessary though. These sorts of problems normally arise when you are doing stuff like logging, and you end up with many millions of records, usually for inane stuff that you didn't really need to store anyway.

In normal usage, I wouldn't worry too much about the stuff you described.

Having plugins installed and not activated is mostly a security footprint problem.