The first thing I'll say is that the paperwork and HR process to administer this was a pain in the ass.
The second thing was that we found ourselves in a bizarre situation where we negotiated a salary with him, then found out afterward that we had to pay him more than he asked for because the OPT rules require employers to pay the immigrants based on published salary rates for professions. And even though our industry doesn't place a high value on a graduate degree, the published industry salaries for OPT hires with graduate degrees is substantially higher.
Three primary attractions...
(1) 7.65% employer exemption for SS & Medicare. And, the foreign worker gets a 7.65% raise.
(2) Possible top students for the median salary.
(3) Most will not quit if hit with salary covered overtime each week.
Also, the foreign students use OPT to roll into H-1B jobs.
H-1B is the turnpike to a Green Card and Permanent Residence, which is almost as good as citizenship, unless you want to work in a Classified military or intelligence job.