lol Trixar is right, but in this application time does move at the same speed.
Concerning the initial question, yes, the difference is neglible when looking at one line of code, but my main concern is really efficiency. If there is no point in making mIRC perform commands for identifiers then why do it? One line is fine, but if a person adopts this method then there are way more than one line doing this and they add up quick.
My philosophy is make mIRC work as little as possible in every tiny bit of code you write because it all adds up.
$+ is used to combine an identifer with something, if it's not an identifier then you can just hardcode it.