If it’s an amplified Antenna then it could help you keep locked to the satellites while riding under tree cover. Personally, I’ve never felt it that necessary on the bike.
Unfortunately I do need to use one in the car because the metalized screen makes a complete mess of reception.
I lost satellite reception far more often using the Nav II (2610) than when I was using the SPIII.
That said, I'd positioned the NavII on a Migsel mount above the speedo, so if I was heading north I was shielding it more than the handlebar mounted SPIII.
Fitting a remote (unpowered) antenna improved the situation a lot. I fitted mine under the black plastic 'beak cover' on my Adv.
Good prices and great service. A genuinely good guy to deal with, in my experience and I have no connection other than being a very satisfied customer.