Some are large like the Community of Christ (formerly RLDS) which unfortunately is becoming more liberal and following that trend which also affects some other denominations. Some are very small. A missionary in our mission met some Strangite Mormons of which there are only 200 or so left.
Schisms in groups and Doctrines are found starting in the NT shortly after the ascension of Christ. A huge portion of Paul's letters are intended to correct some of the splintering that was occuring. The Book of Mormon is replete with groups that splintered away Doctrinally. Some return and some don't.
Even in Jesus time they had schisms it is nothing new!
The rebellious souls always want to revise the program