Almost every tool a business buys today is delivered as software-as-a-service (SaaS) — billed monthly, accessed in a browser, updated automatically. Yet plenty of work still runs on traditional, installed software. If you're deciding what to build or buy, the difference between the two models shapes your cost, your control, and how fast you can scale.
This guide breaks down how a SaaS platform actually differs from traditional software application — across deployment, cost, maintenance, scalability, data ownership, and security — and where AI is now bending the comparison.
What is a SaaS platform?
SaaS (software-as-a-service) is software hosted centrally by a provider and accessed over the internet, usually through a browser, for a recurring subscription fee. There is nothing to install: the provider runs the servers, ships updates, and handles security, while you simply log in and use the product. Slack, Salesforce, Notion and Shopify are all SaaS platforms.
Because the provider carries the infrastructure, SaaS removes the large up-front cost of buying hardware and per-seat licences — you pay for what you use, and you can usually leave when you want.
What is traditional (on-premise) software?
Traditional software is installed and run on hardware you own or control — a desktop, a server in your office, or a private data centre. You buy a licence (often a one-time fee per user), then take on installing, maintaining, securing, and updating it yourself. Classic ERP suites, on-premise accounting systems, and most desktop applications fall in this camp.
That ownership cuts both ways: you control the environment and the data completely, but you also carry the cost and effort of keeping it running.
SaaS vs traditional software: the key differences
Deployment and installation
SaaS requires no installation — you sign up and start working. Traditional software has to be installed and configured on each machine or server, along with the operating system, database, and security layers it depends on.
Cost model
SaaS spreads cost into a predictable operating expense: a monthly or annual subscription. Traditional software is typically a larger capital expense up front (licences plus hardware), with ongoing maintenance on top. SaaS lowers the barrier to entry; traditional software can be cheaper at very large scale where you'd otherwise pay per seat indefinitely.
Updates and maintenance
With SaaS, the provider ships updates centrally — every customer is on a current version without lifting a finger. With traditional software, upgrades, patches, and infrastructure upkeep are your responsibility, which is a real burden for teams with limited IT resources.
Scalability
SaaS scales on demand — add users or capacity and the provider's cloud absorbs it. Scaling traditional software often means buying more licences and provisioning more hardware, which is slower and more capital-intensive.
Customization
Traditional software can be customized deeply because you control the codebase and environment — useful when your process is genuinely unique. SaaS trades some of that flexibility for speed and simplicity, though modern platforms increasingly expose APIs, configuration, and app marketplaces to close the gap.
Data ownership and security
With traditional software, the data sits on your infrastructure and stays under your control. With SaaS, your data lives with the provider, so vendor trust, contractual terms, and compliance (where data is stored, who can access it) matter. Reputable SaaS providers invest heavily in security — often more than a small business could alone — but you should still read the data-processing terms before storing sensitive information.
Architecture: multi-tenant vs single-tenant
Most SaaS runs on multi-tenant architecture: many customers share one application and database, isolated logically. That is what makes SaaS economical and easy to update. Traditional software is usually single-tenant — your own dedicated instance — which gives isolation at a higher cost to run.
Where AI changes the comparison
AI has widened the gap. Modern SaaS platforms ship AI features — copilots, summarisation, search, predictive analytics — to every customer the moment they're released, because the model and infrastructure live on the provider's side. Replicating that in self-hosted traditional software means standing up your own model infrastructure and MLOps, which few teams want to own. For most businesses, the practical way to get production-grade AI is through a SaaS platform built for it. (If you're building one, see our guide to building an AI SaaS product.)
Which one should you build?
Build or buy SaaS when you want speed, low up-front cost, automatic updates, easy scaling, and built-in AI — which fits the vast majority of products and businesses today. Choose traditional / custom software when you need deep customization, full data control, or offline operation that a shared platform can't provide — often delivered as a bespoke custom software build.
For most founders the answer is a SaaS platform, and the real question becomes how to architect it well — multi-tenancy, billing, security, and an AI layer that earns its keep.
The bottom line
SaaS wins on convenience, cost-to-start, scalability, and access to AI; traditional software wins on control and deep customization. The two aren't enemies so much as different trade-offs — and increasingly, the differentiated parts of "traditional" software are rebuilt as SaaS anyway.
Thinking about building a SaaS product? Read our founder's guide to SaaS platform development, or talk to us about SaaS development — we've shipped multi-tenant platforms with billing, dashboards, and AI built in.
