(I want to preface by saying that this information can be great for anyone, but of course my content is geared towards doulas and other birth workers)
Many doulas have trouble getting their business started financially. You have to spend hundreds (sometimes more) on training, books, supplies, marketing, a website, etc. Add that to the fact that many doulas are taking their first clients for free or significantly undercharging for their services. Most doulas are in the hole or barely breaking even in their first year.
Establishing business credit can offer you some cushion when it comes to financing your business-related expenses. Some doulas want an office space to make providing services easier, but can't quite swing the monthly expense until more money is coming in. However, since they can't offer services in the capacity that they'd like to, the money isn't flowing. Leaving them waiting years to obtain an office space. Having business credit can help with that.
Some people wait until they've finished their training to start putting their business together, but I recommend starting sooner. The longer your business has been established, the bigger the benefit. You build a presence, a following, and more time as an established business looks better to credit lenders.
Are you interested in a little more information on building business credit? You can get my E-Book for $4.99