I notice it a lot with some of the more loquacious mid-pack riders, at least in my area. Many of the stickers are clearly custom made to imitate the actual pro stickers on team bikes.
What’s the deal here? Is there an actual practical reason or is this just a personality thing?
Looks pro, people want to feel pro.
I need to get a Fred, DDS sticker for my bike. Would be fire. 
When I was racing for a Development Team we all had the same bike, so the stickers were somewhat useful in making sure everyone knew whose bike was whose. It also allowed the mechanic to know the owner of each bike, which was useful in the hustle and bustle of an early race morning.
I imagine many local club teams experience a similar issue if everyone gets the same deal on a bike/helmet/other gear.
This makes perfect sense and must be where the trend comes from for folks who aren’t riding similar bikes to their team.
It was as a thing in our club before my time, because it seems like half the bikes have them including some really fast folks.
If you want one, get one. #onelifetolive
I have my name on all of my bikes. Some right on top, some in inconspicuous spots. Mostly just because I like it, but partly for identification.
As others have said for most people it’s a inexpensive way to feel a bit more pro and customize your bike.
As a rider for a team with bike and wheel sponsors it’s also nice since all of our bikes look very similar making it easy to mistakenly walk away with a teammate’s bike after a race 
so having a little sticker is just a little thing that can grab your attention before you grab the wrong bike and walk a way.
Where would one obtain said decal? Asking for a friend…
Free speed? 
My friend says “thanks!”
I ride in some big groups and must confess to more than once name decals have saved me from the awkward “what’s your name again?” to that guy I’ve ridden with 100 times . . . .
For pros its branding, for the rest of us think of them as name tags 
I think this follows along the lines of regular Joes and Janes that have “Request to Follow” on Strava. Simply an overinflated sense of import it seems? I don’t understand that one at all…
I have never thought of this but makes perfect sense. 
I have request for follow on for privacy purposes (e.g. I’d prefer not to have my location and normal travel routes available to be scraped, and sometimes I ride mtb routes that are of debatable legality)
This is a good point, I always have a hard time with names.
I’d say this is entirely sensible, especially if you have a high end bike and a penchant for posting pictures of it on social media