Should I be worried about ‘overhead’. What is it and how much is acceptble?

Noticed that my wp_options table shows varying levels of overhead at various times. NO other table does, just WP-Options.

I can’t seem to track it down to an individual plugin but it shows up more regularly the more plugins I have activated.
I notice the value changes up and down depending on what page I have last viewed on my site.

Can someone explain if this is normal. Should I ever get overhead or not? And if it is normal, what is an acceptable level in WP-options?

Thanks
Ross 🙂