If you're trying to get professional affiliates to market your business, sure, use third party software. Most the affiliates know the systems already and have some level of trust in it. Plus the software will provide analytics, payouts to various countries, tax guidance, etc.
Our program is primarily a referral program for existing customers. There's no separate affiliate account and credits automatically offset the fees we charge. Plus I like Stripe and don't want a bunch of third-party PHP crapware invading our already complex billing system. DIY was really the only option.
The things that make our customers want to refer others are not necessarily what will work for anyone else. Our current referral system would never fly with the porn affiliates, but also an impersonal "make $ fast!" affiliate system would never resonate with our customers.
A basic referral tracking system is super easy. Give users links they can share; clicking on the link puts a value in local storage; pass that value along with signups. Offer something meaningful to new customers who come in through a referral (for us, it's a discounted first month). If you're just trying to increase word of mouth spread, that's enough to get started.
Obviously I’m not getting the exposure of shareasale, impact, etc from being on their platform, but I can still sign up for them once I’ve validated that affiliate works for high ticket item hardware.
I've been in the digital and affiliate space for well over a decade and have run programs from the tiny to the massive. Platforms like Impact, SAS and others are great, but if you're looking to get started and don't want to break the bank, let me know. It isn't a business, just a super simple platform for running a program that I built for my own use and could easily be used by others.