Hey @anon82684441
here is a great answer: Estimated effort vs. actual effort - how can I compare? - #2 by Emily_Roman
And here is a sample layout as well: Allocating hours, how to do this? - #2 by Andrea_Mayer
The sum feature works great and I usually work with reports as well.
At our company we usually work with a time tracking tool on top just to get a key overview on the real-time tracked as sometimes team members forget to update something. (Now this obviously depends on your company and set up, if employees or freelancers, etc)