The idea of Batman having sidekicks like Robin is a contested topic, because it raises questions about the ethics of the vigilante using young children in his war on crime. One argument is that having Robin as a sidekick prevents the Dark Knight from crossing dangerous lines during the course of his vigilante activity.
Having a young sidekick also stops Batman from self-destructing. That has actually occurred on occasion, particularly when Batman serves as Gotham's lone guardian, as Nightwing pointed out in Robins #2 (by Tim Seeley and Baldemar Rivas). It's a long-held belief of the original Robin that Batman needs to have someone by his side, and this belief has led Dick Grayson to influence Bruce Wayne to allow others to take up the mantle of the Boy Wonder.
Jason Todd's History With Batman Is Proof of Robin's Necessity
The reasoning comes up in Robins #2, when they have just been told by Batman not to investigate the mysterious villain who is targeting them. Dick pins this down to Bruce being afraid of something, as evidenced by the Dark Knight's anger regarding the situation. Nightwing then tells the others that Batman needs a Robin to stop him from falling into the darkness, even if he doesn’t realize it. Despite having a difficult relationship with his mentor at times, Dick believes Bruce requires a Robin to help keep him grounded.
That can be seen in the Pre-Crisis origin of Jason Todd, which involves Dick Grayson much more than later origin stories for the second Robin. Here, Jason was part of an acrobatic family known as the "Flying Todds" who help Dick's Robin investigate the crimes of Killer Croc, who was extorting their circus. Unfortunately, the involvement of Jason’s parents in the investigation results in their murder. Although Batman and Robin ultimately defeat Killer Croc, Jason is left an orphan, and Bruce adopts him as a young protégé.
After he helps Batman defeat the Joker, Jason is officially given permission to assume the role of Robin after Dick gifts him his old costume. In Batman #368 (by Doug Moench and Don Newton), Dick tells Jason and Bruce that he is giving up his old sidekick identity in favor of fully embracing his leadership of the Teen Titans. Even though Dick knews he had outgrown the role, this demonstrated an awareness of how important Robin is to Batman. Jason’s origin changed in the Post-Crisis continuity, but the sentiment shared by Dick and future Robin, Tim Drake, became the leading catalyst for Tim's own origin story as Robin in A Lonely Place of Dying (by Marv Wolfman, George Perez and Jim Aparo).
Tim Drake Pleaded With Nightwing to Resume His Robin Role
Set shortly after Jason Todd's murder by the Joker, Bruce’s crime-fighting had become more reckless and dangerous, leading both Nightwing and Alfred to become concerned. Tim Drake, a fan of the Dynamic Duo who had deduced their identities, reached the conclusion that Batman needed a Robin to keep him stable. The young Tim eventually tracks down Dick Grayson and shows him pictures of Bruce’s recklessness, pleading with the original Boy Wonder to take up the mantle once again. Dick agrees that Batman needs a Robin, but is not willing to personally fill the role. Nightwing brings Tim to Bruce’s attention as the three foil a plot by Two-Face. There, Tim makes a convincing case to be trained by Bruce to take up the vacant role of the Boy Wonder, and a new Dynamic Duo is born.
Even though Dick outgrew the role of Robin to pursue his own path, the original Boy Wonder knows the importance of the role in keeping his mentor grounded. A lone Batman without the support of sidekicks or Bat-Family members could easily cross the moral lines he has set up for himself. He could even die prematurely without a sidekick to anchor him, and no one is more aware of this than the original Robin himself, Dick Grayson.