I'll make a couple of statements because I've dealt with some. One a very good one.
This guy did not have to travel as far as I knew and was basically phone support. When I told him his product didn't work and blew out our devices when it switched ranges, he didn't believe me at first. A scope at the inputs proved it. He developed a quick fix and sent it to us but it rendered other functions of the instrument useless. They then engineered a permanent fix and did it free of charge.
So, there is this two-way communication going on.
In other cases your selecting an instrument and you want to make sure it meets the requirements, so the application engineer comes to the rescue.
Then there is something you never did and your at the application engineer's mercy to teach you what you need to know to do it right.
Watch out for the sales guy that just dumps a bunch of catalogs on your desk. We got the free use of an orbital welder because we bought/buy so much stuff. So, that sales guy provided the service and training. We had to buy a few consumables. Yep, that was the same guy that dumped the catalogs on your desk.
The application engineer can give training seminars which may even be hands on. They may go to shows with working gizmos.
There is a forum on
www.digikey.com which gives some examples what an applications engineer does. In that particular case, they make videos and answer questions. Take a look at digikey's training modules.
This is from the "other side" or the user of an application engineer's view.
Some have the view of how many are you going to buy if I help you while other's like Bob Pease (RIP) will help the competion or anybody that asks.
My take.