The script supervisor is a regular feature of large movie productions, but an expendable one for smaller productions. Does this make any sense? No, saving money by canceling this on-set position is short-sighted. It shows, that a lot of people don’t really know, what these droll creatures are good for on set.
Ever been editing and swearing because the most wonderful shot was utterly useless for the continuity with the prior picture didn’t fit at all? Ever spent hours matching a mess of film clips with the proper shot?
This means the opposite is key: Especially during the “more chaotic” shootings, where a lot of material is produced in short time, you should rely on a script supervisor, if you don’t want to completely snap in post-production.
A decent statement on the issue: http://www.premiumbeat.com/blog/why-a-script-supervisor-is-essential-to-your-films-success/