A custom Visitor ID can be used on sites where you have unique way to identify visitors. A custom method implemented to identify visitors by setting the
s.visitorID variable which can be up to 100 alpha-numeric characters and must NOT contain a hyphen.
There are some benefits to setting the custom visitor id. The main benefit is that you are 100% in control of how visit(or)s are tracked. Another good reason to do this is if you already have a visitor id infrastructure in place on your site, setting Adobe Analytics’s visitor id to what you already have can potentially make it easier to tie data to or cross-reference data between Adobe Analytics and other places that utilize that visitor id.
Beyond that, IMO there are basically no benefits to setting it yourself. On the other hand, some warnings should be raised
Setting a value in
vid or equivalent does NOT cause Adobe Analytics to update the visitor id in its cookie. Adobe Analytics continues to generate/output the visitor id in the cookie and then on Adobe Analytics server, and it simply overwrites that value with your visitor id for that hit (on the backend, on the collection server). But it does NOT update the cookie with your new visitor id.
The implication here is that if you want to set the custom visitor id, you are essentially putting the responsibility on yourself to keep track of the visitor. So, you must have your own infrastructure in place that not only generates the id, but preserves it and ties it to the visitor, so that it can be output on every page the visitor views – including if the visitor navigates between multiple domains your tracking code is implemented on (if applicable).
If you do not do this, then the visit(or) will break and count as a new visit(or) going from page to page, or when the visitor hop from domain A to domain B. How often the break actually occurs is directly tied to how often you are actually outputting the visitor id yourself (with a correct value). For example if you only set it on first hit, and then on never set it, the visit(or) will break once, because from 2nd hit + Adobe Analytics will just default to using its own generated visitor id.
To put this into perspective, make sure you are absolutely confident about your methods for generating and keeping track of visitor id values before doing this.
So for example, yes, you can use
vid param show up in the request to Adobe Analytics (look at the request sent to the Adobe Analytics collection server with a packet sniffer, or with browser addon or dev tools net/traffic tab).
vid param, because the js library already does it. Although for QA purposes, you can check that it is there with your value on a given request.
s.tl trigger, you assign a value to it, e.g.
s.visitorID="[my custom visitor id here]";
Where specifically you set it, depends on how you have implemented Adobe Analytics. For example, if you have implemented Adobe Analytics through DTM, and you have your custom visitor id exposed on your page before the DTM library is loaded (e.g. some data layer property, or in a cookie), you can create a data element that grabs that value, and then in the Adobe Analytics > Tool Config > Cookie > Visitor ID field, you can specify your data element, and DTM will set it for you (but you are still responsible for making sure whatever source the data element draws from is there)
And again, note that even if you set it, you will still see Adobe Analytics’s default generated id in their cookie and request urls. The override happens on Adobe Analytics’s collection server, which you do not have visibility into. To verify that Adobe Analytics is actually using your custom value, you will need to export it from Adobe Analytics (e.g.with a data warehouse export).