HR/Recruiter

Would be good if you could state your intent, so we can give you a more targeted answer.

In general, recruiters (especially in MBB) typically have 2 main functions.

a) Coordination: i.e. they organize and manage recruiting events, administrate the recruiting process / slot interviews & online tests, ensure pass/fail decisions are made and communicated, and act as general contact point for prospective candidates.  

b) Screening: they review the flood of applications and decide who gets and interview vs. not, or (esp true for MBA recruiting) channel applications to reviewers who then shortlist.  

It's important to note that in most Tier 1 and 2 consulting firms, recruiters do not get involved / have any direct mandate regarding case interview assessment. 

This means you reaching out to them can sometimes be of a little help to secure an interview invitation (esp. if you're profile is border-line to get invited), but that's also where it stops.

1. What is the role of recruiters in large firms? Internal recruiting teams conduct all recruiting admin activities end-to-end (processing applications, screening, scheduling, etc.)
2. Do you recommend reaching out to them? Better to reach out to consultants in order to secure a referral. 

1) What is the role of recruiters in large firms?

To recruit! They bring in candidates, screen candidates for initial interviews, etc.

2) Do you recommend reaching out to them?

Yes and no. Not directly, as it is unlikely to bear fruit.

Networking is key here. Start with other consultants at the firm and work your way towards either being put in touch with the recruiter or getting a referral.

Assuming here you mean HR people, not the hiring managers.

1. They plan the recruiting activities for their companies

2. Depends on the objective, but usually no. But you should state your objective in the question.