Deleted scenes are not normally seen as canon having been altered or cut from the film because of story revisions or for time constraints and emotional impact. So, it largely depends on the context of the scene, and how can it fit without altering the events of the film if you deem it still useful for the film. Some deleted scenes from
The Lion King II such as Kovu hunting a bug and Vitani and Nuka reporting Kiara's presentation to Zira can be useful because it shows Kovu's training and reveals the age gap between Kovu and Kiara. It can easily fit between the title card and the scene of cub Kiara running out of Pride Rock. However, they were deleted because of pacing reasons according to the director. (
Read here.) However, some deleted scenes may have the original characters interacting with the deleted characters, which is definitely not useful for the films since those characters were dropped from the films and unless a name drop occurs, those characters don't exist in the films.
Other scenes could have deleted or altered lines, which are not really useful since the writers created newly written lines for the characters, an actor ad-lib the dialogue, or the line(s) was simply not useful. Lastly, some deleted scenes are often the earlier stages of the finalized scene like Simba's fight with Scar where Scar is engulfed in fire. Overall, I like seeing deleted scenes because it reveals what the filmmakers had to go through in order to develop the characters and the story, and discover for themselves what the characters and the story is about. While more story content is always good when deepening the story, less is more is an abiding principle during the filmmaking process.