Except on the shortest of trips, I always use ear plugs while riding motorcycles because they protect from hearing damage that is caused by riding motorcycles. The damage is not caused by street noise; rather, is caused by the high frequency wind noise that riders encounter. Helmets and wind screens do not reduce the damaging noise. There are countless articles on this topic and they all seem to point to the same conclusion. That is, hearing protection is a must for the motorcyclist. Here is a LINK to a good article in BikeBandit regarding ear plugs.
There are many types of ear plugs on the market, but fitment and the Noise Reduction Level (NRR) should be considered first and foremost. I've used disposable Hearo Ear Plugs for many years. They are a bit larger than most brands and, therefore, seem to fit in place better. They also have a considerable NRR of 33dB. To put that in perspective, 33dB reduction is the highest reduction level that you can get in ear plugs while 31dB is the highest reduction level that you can find in ear muffs. I know this because I frequent the rifle range with my NRR 31dB ear muffs and with my NRR 33dB Hearos plugged in for added protection.
Can you hear everything you need to hear while wearing ear plugs? The answer is yes. Ear plugs do not eliminate ambiant, low frequency sounds. You'll still hear the cars and horns and sirens. Plus you're able to carry on a conversation with your riding buddies while wearing plugs.
There are also many permanent solutions for ear plugs; some with custom fitting. I'd support that, but in my case I'd lose them ... and the fitted plugs are naturally more costly. I'll stick to the disposable Hearos, which just cost me $5.49 for 14 pairs. So as not to run out again, maybe I should buy them in this sized container.