I was lucky enough to invest in Mixmax, Pipedrive, Salesloft and HelloOffice after I was already a user/customer. That makes it kind of a no-brainer if you also see strong metrics and find out they have a great CEO.
We also use Algolia as the core search engine for our 40,000+ pieces of content in SaaStr which is fun, however, this functionality wasn’t fully available when I invested way back at $12k in MRR.
Also, while I did not use Talkdesk or Logikcull or Rainforest QA as a customer before I invested, I had deployed/worked with legacy versions of similar products. That certainly helps make the benefits over legacy systems much more tangible.
Does it matter if you are a customer of products you invest in? No. But once in a while, it gives you a leg-up on parts of the due diligence process, and lets you move fast. That can only help.
It also makes investing more fun.