Loss prevention was foremost in my mind when deciding how to mount electronics. I spent $2000 on a unit I won't be putting in-dash. Something that expensive attracts a lot of attention; I don't want it to grow legs and run away! A number of boat models I've checked secure the unit in a panel that is then mounted to the console with six to ten screws. All of the ones I checked are sheet-metal screws, not machine screws. A thief with a cheap screw-gun can quickly free the entire panel, cut all your cables (quicker) and leave with your unit still in the panel. You'll discover a big hole and a bunch of cut cables (Xducer, HD Xducer, network, power, and maybe NMEA). Replacing all those is a lot of work and expense even beyond the lost unit. I've seen photos of the case I described here, and the same for bow panels.
I put the big $$$ unit on a removable mount so I can remove and secure it when it's at risk. I also get the advantage of controlling angle for glare.
I put a less expensive unit in-dash, THEN swapped out all mounting sheet metal screws for machine screws with lock-nuts installed on the backside. Now, the machine screws won't back out without getting a wrench on each of the locknuts. This makes it much more complicated for a thief with a screw-gun and the idea of taking the panel with unit intact. He can spin the screws, but they won't back out unless he takes the time to get a wrench on the locknuts under the console.
Thieves want a quick steal to reduce the risk of being caught, and may walk away when their standard method doesn't work. There is still a risk I could lose the in-dash unit, but I've made it more difficult in hopes that the thief is in a hurry and lazy.