I always hire for a probationary period.
Some people can hide their true colours in interview...
A good example of why you should do it?
One guy got hired simultaneously by TWO of my clients for full-time work (he claimed to each of them that he was moving or ill or some reason to be a bit patchy in his initial attendance I think). He was also quite aggressive to deter people from asking him questions. His misfortune was to be sitting right next to me in both companies which led to some interesting questions from me.
I'm not sure that either of the companies had him on probation, so actually firing him would have been quite messy and expensive, and I think that he was going to string them along for a month or two and then have them just get rid of him quietly to avoid difficult court cases.
However, since I pointed out to him that I knew extremely senior people in both companies (the MD of one, for example) that if he didn't resign without taking any money I'd be quite prepared to stand up in public court and say was a fraud he was...
Anyway, thankfully, he went...
(And yes, I did tell the senior people so they had to stop payroll given the fraudulent nature of his sign-on.)