Marko Mäkelä wrotes on Mon Mar 8 07:03:51 GMT 2010
In the TYP file, you can define default names for POIs that lack a  
name.

And that's the only use of it.

Does it only affect the map display  (when you move the cursor over the icon)

yes and no, the replacement name is shown also as name if you enter the POI (and may be also saved if you save the POI as Waypoint. I have not tested it.)( In addtion to it during opening a single POI by pressing ENTER this name will also be displayed for some seconds in the status bar. Thats almosts(for some types not) the case even the POI has already a name)

, or does it also control whatis displayed in the POI menu?

No.

I have had a look into a map (openmtbmap de), and as far as i can see, only non-standard poi-types creates these multiple "other" categories. With non-standard i don't mean these extended-type(or 3-Byte types). Non-standard means types which are e.g. not part of the standard-typeset of GPSmapedit or cgpsmapper.

e.g for shopping it is:

0x2E01    Department Store
0x2E02    Grocery
0x2E03    General Merchandiser
0x2E04    Shopping Center
0x2E05    Pharmacy
0x2E06    Convenience
0x2E07    Apparel
0x2E08    House and Garden
0x2E09    Home Furnishing
0x2E0a    Special Retail
0x2E0b    Computer/Software

Types like 0x2e1f creates one "other" entry in the categories submenu. The replacement text "sporting goods" from the type-file will only be shown for seconds in the status bar if you press enter for opening the POI.

I have to mention, that i only have a 60csx to look at it so it may be different on other gps like oregon etc.
Gert