Using a template for your portfolio does you and your work a disservice. I say it all the time. But you might assume (given the fact that I co-founded two portfolio tools that don't offer templates) that I say this to push my products.
While I do want you to use my products, I'm not pushing the anti-template agenda for that reason. It's this belief that inspired my tools in the first place.
If you use a template for your portfolio, you're forced to retrofit your work into someone else's layout. You're making compromises and limiting yourself before you even begin.
2. You're making it harder on your future self
If you lock yourself into a template, you're less likely to keep your site updated year after year. Why? Because changing templates is a hassle. If you decide you don't like one element of the template (the navigation or homepage layout, for example) you need to change the entire template and essentially rebuild your site. That's daunting. If you use a flexible layout that allows you to customize, you can easily spend 30 minutes here and there updating design elements, adding projects and keeping it fresh.
3. Because why would a designer use someone else's design?
When you use a template, we can usually tell you're using a template. If you're a designer, that's a bit cringeworthy. You design for a living but you're using someone else's design for your own site?
Of course, not everyone who needs a portfolio is a designer. If that's the case, there's nothing wrong with working from a provided foundation. It's still ideal to customize as much as possible to suit your work, however. (And if I may be so bold, I would suggest Carbonmade for your site in that case. You'll build off a starting point, but you can easily customize your site without any design or coding knowledge. )
4. Because this is your one chance for complete freedom and control
Assuming you do creative work for a living, your portfolio is the one chance you have for full control. No client feedback. No stakeholders, template restrictions or brief to meet. You finally get to tell the story of your work the way you intended it to be told. Why pass up that opportunity?
Whether you use my tools or not, I encourage you to create a website especially for your work. Create case studies that present each client and piece of work like a magazine feature. Design a homepage that showcases your work in the best possible way, whether you have one project to show or 10. Create an About page that conveys your personality.
A template may be tempting, but in the end it's a cheap solution with cheap results. And no matter your experience or skill level, your work deserves better.