Because of a crowded handlebar, I use a topeak bar extender on one bike. The handlebar space is limited by in-line top bar brake levers, and handlebar bag straps. If I modified the top bar levers to get them further from the stem, I wouldn't need the bar extender, but it was much easier to just put on the bar extender.

And I got a wonderful benefit from the bar extender - my headlight is way out front, so that the bike's cables do not cast any shadows. The topeak bar extender has reasonable adjustablilty, and holds position well. I truly prefer the look of gadgets on the handlebars instead of having the bar extender cluttering things up, but not enough to bother reworking the handlebar tape and cables to eliminate the need for the extender.

The extender takes up about one small gadgets worth of room on the handlebar, and gives you 2 to four full size gadgets worth of room in return. It is possible to mount the extender on the stem as well.