Do agencies help with brand deals, type of content, and posting strategies?

Hello folks!

I often see content creators/influencers put 'Managed by xyz" on their instagram bio. I am wondering how do these agencies help influencers? Do they help with closing brand deals, provide strategies on when to post content/story, or what type of reel to make and hashtags to use for engagement?

And does that mean they charge flat fees/commissions for that help, if so around what % on an average?

And if I am totally missing the point – why do influencers get represented by agencies?

Thank you for any insights!