OpenType with no 1000 em

Glyphs
1

When generating an OpenType font in FontLab that doesn’t have an em-hight of 1000, it gives next error, while Glyphsapp does not. Does it realy matter somehow?

http://s10.postimage.org/z87yy5n09/Font_Lab_message.png

Is it recommended to work with 1000 em? If yes, it it recommended Glypsapp should also give a warning.

2

There was recently a discussion about that on typedrawers