Waypoints have to be indexed by the operating system.
Waypoint are graphic images displayed on your map.
All these things take up memory, and require additional
processing.
When your map screen refreshes, do you think it will refresh
quicker with hundreds of waypoints, as compared to none?
The more waypoints you have, the slower your system
is going to be.
The slow down may not be discernable to you over time,
because you get used to it. Also, the 1198 has a pretty
fast processor, and can handle more than say, an 1197.
If you think your system is not slowed down by
your waypoints, then do a test:
Back up your waypoints, then erase them from
your unit. Then, put in an SD card in with no
waypoints on it, and see the difference. Your system
will fly.
On my 1197, I had far too many waypoints, and I could
see things slowing down, dramatically.
Removing some of them speeded things up.
It's the same principal of your PC desktop.
Fill this thing up with ICONS, and you will have less
physical memory to use for other things. The machine
will also take longer to boot up.