The first ICO among crypto-currencies appears in 2014 year and it was Etherum, but only this years on the wave of Etherum's stable growth ICOs became blooming. Why do they appear? People want to make on other people's wish to become rich fast, just like it happen with Etherum holders. Generally it's just start ups which are only promising profit to investers, but don't guarantee it. Only 2-3% of this projects really worth and have a chance to become successful. So, don't hurry to invest in every that you see. Actually the number of ICOs that are just going to be announced is huge. But the most of them will not bring any money indeed.
Everyday, several coins/projects are being launched to have their PRE-ICO or ICO.
The major objective that I can see for these pre-ico is to earn initial amount of funding for their project to commence their plans.
If unfortunately, the project turned out to be scam, the people involved will just disappear along with the cash collected and the investors are left regretting that they invested their hard-earned money.
Everyone can have their own pre-ico/ico, so it's up to the investor to check the authenticity of the project and their viability.
Normally, if the project is legit, pre-ico will really give you benefits over the ico stage, if that project turned out to be successful.
And a lot of times, as there are several factors that influenced the fate of the coin, it's difficult to predict the outcome of the project.