In general, Singaporean PRs are permitted to live, work, study, serve, start a business and retire in Singapore indefinitely.
PR status is robust in practice but not absolute, and individuals could have their PRs stripped and deported from Singapore if convicted of a crime.
[1][2] PRs are also subject to an active Re-Entry Permit (REP) if they wish to leave Singapore for any length of time for any reason.
The government does not disclose its evaluation criteria or decision processes beyond broad generalities, such as long-term citizen population-related goals.
[5] PRs (age 15 and older) are issued blue colored National Registration Identity Cards (NRICs), in contrast to Singaporean citizens which are in pink.