Sage People is the enterprise end of Sage's people line. It is built on the Salesforce platform, which is the single most important fact about it and explains most of its strengths and most of its costs.
What it does well
Multi country is the reason to buy it. Different policies, different leave entitlements, different compliance regimes and different currencies across a dozen countries, all in one system with one org chart. For a US headquartered company with teams in Canada, the UK and the EU, this is the problem Sage People was designed for and it solves it properly.
Because it sits on Salesforce, the configurability is close to unlimited. Workflows, fields, objects and reporting bend to your process rather than the other way around, and if you already run Salesforce your admins are productive on day one.
Where it fits
Organizations from roughly two hundred to several thousand people, operating in more than one country, with an HR operations function and a budget for it.
Where it frustrates people
Payroll is the same story as Sage HR and it catches people out just as often. Sage People is not a US payroll engine. It integrates with payroll providers, and North American customers run ADP or an equivalent alongside it.
The Salesforce foundation cuts both ways. That unlimited configurability means implementation is a project measured in months, usually with a partner, and the reviews are consistent that the cost lands well above the initial quote. It also means you inherit Salesforce's release cycle and its administrative overhead. For a company that wants HR software to work out of the box, this is the wrong product, and the ones who are happiest with it are the ones who arrived knowing that.