I keep the SBC in my 35mm kit bag. I use the meter in the camera, though, and the SBC for some intangible security blanket. With roll film, i try to trust the camera meter and judge that the average light is about right or needs a twist of the ex comp. dial in the camera. When i don't feel secure, i bring out the SBC. The cameras i use, manuals all say make a judgement based on scene lighting and make the ex comp accordingly. I really like the ergonomics of using the SBC. A fantastic meter. (i am a self-confessed analog dial obsessive-compulsive).
For large format, i always use a spotmeter. Since it runs on batteries, i keep a Weston V (calibrated by the aforementioned QLM in Hollywood) with incidence (invercone) accessory, in the backpack i carry for this kit. Incidence-ly, i sure like that Weston meter. But i also love to work with the Pentax spotmeter v. Another security blanket maybe, but i try to make sheet by sheet development decisions based on what i record as zones in the exposed scene.