If you only intend to create one font, and don’t need to use the font for commercial purposes, the Home Edition may be enough. Otherwise, you need the Standard or Professional Edition
The Professional Edition has only two features lacking in the Standard Edition: Decompile OpenType features, and Optical Metrics.
Decompile OpenType features will create a script that can be used to export the OpenType features unchanged, or you can edit them to add more features, or add your own.
Optical Metrics will calculate the left and right side-bearings for (English) fonts. This can be done manually simply by dragging the bearing lines, but it’s an art requiring considerable experience to get the spacing right. Setting left and right side-bearings to a fixed value can be done with Autometrics in the Home Edition, or using the Glyph Transform wizard in the Standard Edition, but letters are all different shapes and require different side-bearings. Open any commercial font and scroll through A-z looking at the bearings in the Glyph Properties toolbar (F3) and you will see how much they vary, e.g. Tahoma:
Left, Right
A -10, -10,
B 151, 46
C 66, 34
D 151, 64
E 151, 67
F 151, 26
G 66, 98
H 151, 151
I 93, 93
J 9, 141, etc.
As you can see, they are nearly all different. Only H and I have equal side-bearings. Amateur designers may benefit more than Professionals by having the software suggest suitable values for them. Pro users, or artistic designers just know intuitively when the spacing looks right, but amateur users often waste far too much time kerning their fonts because the side-bearings are all wrong. If you don’t mind manually adjusting the side-bearings until they look right, the Standard Edition may be good enough for you.
See this thread for a few screen shots of the results of Optical Metrics for different fonts. After using Optical Metrics a few times, one gets to know what value needs to be used to generate a font that is spaced appropriately for the design.
Both Standard and Pro version offer a high level of automation missing from the Home Edition, for creating composites (áéíóú) and transforming glyphs.