I love that phrase, Jon! And I think this is very true about them being 'nice to have'. I didn't include comp titles in my covering letter for my debut. I didn't know at the time (2013) that I needed to. When I went on submission to publishers though, my agent used comp titles (Apple Tree Yard, Precious Thing and The Girl on the Train - this was before that was every comp title for every thriller!)
Publishing loves comp titles because they love any shorthand that can sum a book and its market up quickly. But an agent won't put a submission in the bin unread if the pitch didn't include a comparison.
Thanks Holly, this is great insight. The only thing I worry about is getting the comp titles wrong. I worry it will reflect badly, for example if I put 'will appeal to readers of Ben Aaronovitch's Rivers of London and Mark Hayden's 13th Witch' as a very basic example, that's where I would like to think I am. However, before even reading my submission, I worry that by using such a big name that they wouldn't even consider it, as they'd think I'm a little self-important?
I keep coming back to this, and I think it's a confidence thing. Perhaps I just need to give myself some space from... well, myself!