A consulting company or professional services firm basically 'rents out' their employees to other companies that may need help with a specific task (1) or can't do a task on their own for legal/business reasons (2).

1. Sometimes, a company just needs a specialist to help them achieve their goals with a specific project. Maybe they need the services of an appraiser, or an actuary, or a PR person, or a software developer, or a lawyer with a specific specialty, for a limited time. So, this company asks a consulting firm to 'borrow' someone with the specific skills they need.

2. Consulting agents are often hired by companies to do audits. A company can't really audit itself effectively, since everyone in the company has a vested interest in making themselves look good. Bringing in an auditor from outside allows a more neutral look into how a company is running. This is especially important if the results of the audit will be shared outside the company that requested the audit to be performed.

Usually consultants are brought in to be a hired gun to solve a singular or tightly defined range of problems on things that they are Subject Matter Experts regarding. That subject might be software, engineering, HR related, any number of areas.

To answer the question in a bit more depth, the Big 4 (EY, PwC, KPMG, and Deloitte) have management consultancies. MCs advise company management on how to enact specific changes in their organization. This typically falls into one of three catagories:

• Strategic: High level business decisions, like which markets to enter, which products to launch, which companies to purchase/divest, etc. The big stuff that the C-suite is invovle with.

• Process: How to actually implement a given strategic priority. Like, if you decide to sell a new product, how do you operationalize that? What does your sales model look like? How do you optimize the manufacturing and supply chain? How do you set up a shared service center to handle support issues?

• Technology: The actual software and tech that allows for the change. If you decide that you need new CRM software, how do you actually implement that and get it integrated with your existing technology stack.

The software devs will work with the consultants in the third example - the consultants will do the design and planning to ensure that the business objectives of the technology are met, while the software devs will actually do the coding and implementation to those requirements.

Consultants help companies change or improve their business operations. But it’s a broad directive based on specific case. Often, it means helping companies improve their operations through technology and software, like helping set up and customize a business software platform or even build a custom platform to help the business operate more efficiently… say something like allowing a chain of stores to better order inventory from the central warehouse, or a logistics company to better assign/plan delivery routes; helping an eCommerce company build a better, more effective sales platform that can do things like show customers actual real-time availability and offer alternatives if our, or upsell when they do find what they want (make sure to get ink for that new printer; this belt goes well with those shoes).

It can even be pretty mundane stuff, that’s actually much more complex under the hood due to interconnections… like when my company shifted from gmail/Google calendar & MS Office to a full Microsoft 365 set up that tied network logins to all software, meant migrating literally decades of emails and calendars, etc. and training employees on the new programs.

consultants are experts. since they're really good at what they do, their time is very expensive. it's way cheaper to just use a consultant here and there when you need them, than to hire them to work for you fulltime.