Suspended Execution of Sentence is the cousin of SIS. The court actually imposes a specific sentence (say, 1 year in jail), then suspends its execution and places the defendant on probation. The conviction is on the record from day one.
If probation is successfully completed, the sentence is never served. If probation is revoked, the suspended sentence executes immediately. The defendant goes to jail for the originally-imposed term.
SES is often used when SIS isn't available (because the charge or prior record disqualifies the defendant) but the court still wants to give the defendant a chance to avoid actual incarceration. The trade-off: a conviction on the record vs probationary supervision.