So, I mean, I suppose the real question is: How long a slash is this? How deep? How much blood have you actually lost? How do you define "relatively unimportant"? How easy is it for you to reach that area? Do you have practical experience in patching yourself up, including self-suturing?
If it's longer than four inches or deeper than a half inch, even if it's someplace relatively innocuous such as the front of the thigh and no arteries have been nicked, I'd say you should still go to the hospital, even if you do have practical experience patching yourself up.