Loyalists were Americans who fought on the side of the British and worked with them. It is estimated at least 10% of colonists were loyalist. Do you think they had a big effect?
I don't think they had much of an impact overall in helping the British. For example, one of the reasons the British went and tried to take control of the southern colonies was because they were under the impression that there were more Loyalists in the south and it would be easier to subdue. But they were wrong in that and the campaign turned out badly for the British.
The loyalists may not have had much of an impact in the overall outcome of the war, but in all likelihood, the war would have been shorter if they'd not been helping the British. Something that could have had a big impact in the outcome of the war (or a shorter duration) was if the undecideds had picked and supported a side. I just looked this up not too long ago, and I believe that around 50% of the colonists didn't support either side, especially at the beginning; they just wanted to wait and see who would come out on top before picking a side.
I've heard that the best estimates are that were that there were 1/3 Patriots, 1/3 Loyalists, and 1/3 Undecided. I suspect that the Undecideds had to choose a side eventually as the war "came to them." I am sure the Loyalists impacted the outcome in many ways. I have heard that many wanted desperately to go back to England but as the war went on, they were sort of trapped here.
https://en.wikipedia.org/wiki/Loyalist_(American_Revolution) and other sites I've seen estimate that around 20% of the colonists were loyalists. Many of them fled after the Revolution to other parts of the Empire, especially to Canada.
