Hi
It does matter in some ways.
I posted this here a few weeks ago
Keywords in directory and page names
Underscores are treated as whitespace.
Underscores are not preserved as literal text in URLs
Hyphens are.
Underscores have no use in the English language
Hyphens do
--->>>Reasons NOT To Use Hyphens!!!!!
Hyphens are logically applied text wrapping points.
If you choose to utilize URLs that use hyphen in the address, that URL can, and probably will, wrap if the address is sent by email to others.
Underscores will not.
Dashes are used in math, so searches with dashes in the equation give you another competitor.
Dashes are used in the context of search engine algorithms as negative operators. This means that searches including a dash prefix ("-keyword") will actually prevent that term from being listed in the result
Peace!